PRE FACE .

THE present sheet of the Geolog ica l Survey Map of S cotland was

surveyed by Dr. John % ou n g , Mr. James Geikie, Mr . B . N. Peach,

and myself ; Professor A . C . Ramsay being at the time Local Director

of the w ork under the Director - General, Sir Roderick Murchison. My

share of the mapping extends from the northern edge of the m ap south

wards to a line drawn from the north flank of Pin ba in Hill to Little

L etterpin . Dr. % oung mapped the ground im mediately to the south of

that line,as far as the L en da l Water and the Kin claer Toll - bar. The

remainder of the map to the south was surveyed by Mr. James Geikie,

except the groun d lying to the east o f a line draw n from Da lreoch , 1%mile E . of Colmonell

,southw ard by L ig lea in Glen Tig, to Drumbow ie

Rig,which w a s mapped byMr. Peach.

The northern portion of the sheet,from Ballantrae to Girvan

,forms

part of the area described by S ir Roderick Murchison in 1 851 , and of

w hich he published a Sketch-Map, in which this part of S cotland w a s

fir st brought in to general correlation with the S ilurian rocks of Wales .

(% u a rt. Jou rn . Geol. Soc. , vn .I

Of the follow ing E xplanation, paragraphs 2 , 4, 8—10, 1 7, 20, 25—2 8,

3 2 , and 3 4, have been furni shed by Mr. James Geikie, the rest have

been written by myself. The lists of fossils have been prepared by Mr.

E theridge, Palaeontologist to the Survey. It is proper to add, that the

full details of the Survey of this district fall to be given in the Geologi

cal Su rvey’s Memoir on the Geology of Ayrshire, which is in preparation.

ARCH. GE IKIE ,D irector.

G n o n oec L S % R V E % OF F I CE ,

E DINB% RGH, Ju ly 1 869.

EXPLANATION OF SHE E T 7.

I . ARE A EMBRACE D IN THE MAP.1 . This sheet of the Geological Survey Map of Scotland comprises the

south- w estern maritime tracts of the county of Ayr from near Girvan tothe mouth of Loch Ryan. Along the southern edge of the Map th reesmall portions of W ig toushire project to the northward ; but, w ith theseexceptions, the whole area belongs to the old division of Ayrshire know nas Ga rrick . I t in cludes the mouth of the Girvan Water, the valley ofthe S tin cha r as fa r up as the confluence of the Assel, Glen App, theWater of Tig

, a n d the upper streams w hich drain into the Water ofLuce. The area included in the Map is about 1 10square miles.

I I . FORMOF THE GRO% ND.2 . The physical features of this district present little variety. Thecountry is hilly throughout, the only comparatively level tracts beingthe narrow strips which flank the principal streams. But although thisis the general character of the region, yet, if we take the line of theRiver S tin char, which flows south - w est, w e shall fin d that the ground tothe north of this river is somew hat more diversified than the more elevatedtract of hilly land to the south. This latter may be described as anundulating and sloping table - land, the axis of which runs NE . andS W . through Beuera ird (1 43 5 feet over the sea). Near the northernmargin of the district

,in the n eighbourhood of Ballantrae

,the ground

(300 feet or thereby above the sea- level) begins to ascend gently atfirst for about a mile and a half, after which it rapidly s10pes up from400 or 500feet to a ridge of hills (1 200feet) which overlooks the longstraight valley of Glen App. The highest point in this district isreached in Ben eraird, south of Glen App, from which point the groundslopes away to the south in a series of soft undulations. Nearly all th isarea is moor and pasture land

,the cultivated tract s being almost exclu

sively con fined to a few narrow bands along the course of some of thestreams. The slopes of this undulating table- land seldom show any barerock

,but are abundantly coated w ith peat a n dcoarse grasses

,w hich gives

a bleak and desolate aspect to the country. I n the district north of theRiver S tin char the ground does not attain a greater height than about860 feet ; but the surface generally wants the smooth undulation of themore elevated tracts towards the south, many of the hills being precipitousand abrupt, and showing numerous broken scaurs and crags of rock .3 . Tw o leadin g systems of v alleys traverse the southern uplands of

S cotland, and both are exhibited on the present Map. The one runsparallel w ith the general strike of the S ilurian formations, that is, northeast and south-west ; theother crosses the intervenin g ground transversely

6

in a general north-west and south- east direction. The former, or longitudin a l series, is seen in the dominant valleys of the Girvan, St in char, andGlen App to the latter, or transverse series, belong the numerous tributaries w hich flow from either side into these streams

,as well as those

whi ch,rising on the table - land south of Glen App

,flow down tow ards

the Bay of Luce . With one exception,no connection has been traced

between the direction of the valleys and the lin e of any faults among therocks. The longitudinal valleys ru n more or less along the strike of thestrata, but w ithout adhering rigidly to one group of beds. The Stin cha r,for instance, w inds to and fro over unaltered, metamorphosed, or crystalline rocks, w hile at the same time it skirts, flows along for a little w ay,and then crosses lin es of fau lt. The same features are exhibited by theGirvan. There can be no doubt

,however

,that the strike of the rocks

has guided the course of these streams,and determined the parallelism

of all the longitudinal valleys. The transverse valleys, on the otherhand, are much more sinuous and irregular, and, so fa r as can beascertained, bear little or no reference to the geological arrangement ofthe rocks beneath them. They wind across the edges of the highly incli n ed S ilurian strata, very much as they would have done through anyother group of rocks.4 . The one singular exception to the want of relation betw een thetrend of the valleys and the line of the faults is furnished by Glen App.That valley coin cides with the line of a fracture which has been tracedfrom F innart Bay for many miles inland. This dislocation everyw heregives rise to a marked feature even when the hollow is not occupied by awater- course. This is well seen in the present Map. From the head ofthe Water of App the depression or hollow is easily traced across thewatershed into the Muck Burn. The peculiar straightness of the GlenApp valley is quite abnormal, and serves to distinguish this from the otherlongitudinal valleys, where no connection can be traced with any fractureof the rocks underneath. As in the di strict south of the Stin char, so here,agricultural operations are carried on chiefly in the valleys and along thecoast- line

,the remain ing portions of the groun d being in pasture land.

The fertile fields, the fin e banks of natural wood and other timber, and thecomfortable farm- houses of the S t in cha r valley, contras t strongly withthe bleak stretches of moor and pasture land, and their lonely shepherds

’

cottages,im mediately beyond.

5. The coast -line from the northern edge of the Map, southward to themouth of the Stin char, presents a narrow flat selvage of ground betweenthe sea-margin and a steep bank w hich ma rks a former coast - line, an dsw eeps up in to the hilly ground of the interior. I n on eor two places, part icu la rly at Bennane Head, this level platform is interrupted by the pro

jection of a bold headland into the sea. I n such ca ses, the coast roadwhich lies al ong the platform has to ascend a nd cross the in terruption.S outh of the Stin char, a line of broken cliff descends abruptly upon thesea all the way south into Loch Ryan, and the high road has thereforebeen diverted inlan d so as to rea ch the shore again by the valley of GlenApp.

6. I I I . FORMATI ONS AND GRO% PS OF ROCK E NTE RINGINTO THE STR % CT% RE OF THE DI STRI CT.

A% % E O% S.Alluvium, Peat.

Recen t and Post Blown Sand.Tertiary. Raised Beaches .

Glacial Drifts.

7

Perm ian . Red Sandstone and Breccia.old Red Sanston e (Middl e) .

Red Sandstones and Conglomerates.

Lower Llandovery.Low er S ilu ria n . Caradoc.

Llandeilo .

ME TAMORPHI C AND I GNE O% S .

Miocen e Dolerite dykes .Altered semi- crystallin e strata

,bedding distinct

in some parts.Felspathi c and Porphyritic rocks .

Associated with Felstone.Low er S ilu ria n Syen ite.

rocks. Diorite.Hypersthenite .Diallage rock.Serpentine.

I V. GE OLOGI CAL STR% CT% RE OF THE DI STRI CTSCONTAINE D IN THE MAP.

7 . With the exception of the tw o small patches of Old Red S andstonetow ards the north - eastern corner of the sheet, and the little Permian outlier at Ballantra e

,all the groun d represented by theMap is occupied by

rocks belongin g to the Low er S ilurian series . It will be seen that thecourse of the River Stin cha r very nearly coin cides with a marked line ofdivision in this S ilurian district. To the south the rocks are of the usualcharacter which prevails among the uplands of the south of S cotland .But on the n orth side of the line these strata have been much metam orphosed, and they are pierced by intrusive masses of syenite, felstone,and diorite. E ach of these two areas falls to be described separately .

L ow er S ilu rian .

a . D i strict S ou th Of th e S t i n ch a r Va l ley .

8 . A large fault, w ith downthrow to the north, w hich runs parallelwi th the valley of the River St in cha r in a long sinuous line, from Brackness Hole on the sea- coast to Pium ore on the Stin ch ar (zle. N E . and

forms the northern boun dary of this district. The strata consistof greywacke

,conglomerate, sha le, and occasional bands and beds of

Lydian stone. They have not yet yielded fossils, except some obscure,possibly fucoidal

,markings

,but they are probably referable to some part

of the great Llandeilo series.’ie Greyw acke is by far the most abu ndantkind of rock. It is commonly of a blue or bluish- grey colou r, and variesin texture from a fin e- grained mudstone to coarse - grained grit, whi choccasionally becomes pebbly and conglomeratic . These va rious kinds ofgreyw acke occur in thick beds and thin ner bands, which are usually muchjoin ted ; hence the rocks are not well adapted for building purposes .Occasionally

,how ever

,the joints are less plentiful

,and the greyw acke

might be easily quarried ; but the want of good roads, and the di stancefrom railways, render these rocks, save for local purposes, practicallyvalueless . The greywackes are interbedded w ith lines, partin gs, bands,a n d beds of shale, usually hard, shattery, fin e- grained, greyish - blue,

At Ca irn Ryan , which lies a little to the sou th-w est, on the sam e lin e of stri ke,Mr. J. CarrickMoore fou n dGrap toli thu s foliu m , G . p ristis, G’. tozm'

a,etc. See% ua rt.

Jou rn . Geol. Soc , vol . v. p. 13 Murchison , S i lur ia , 4th ed. p . 155.

8

grey, or green. I n some places these show a rude cleavage, butthis is not common ; they are nowhere rendered suitable for roofingpurposes . Bands of coarse conglomerate occur here and there

,and

one great mass occurs on the north side of the Glen App faul t,form in g the hills of Au chen crosh and Sm irton , Ba lra g ie F ells, etc.Another mass of conglomerate

,on the same strike, forms the bold

headlands between Corsew a ll Point and Milleu r Point,in W ig ton shire.

The nature of the stones in these conglomerates,and their great size,

render this deposit suffi ciently remarkable. The stones and boul ders consist principally of syenite, gneiss, granite, various porphyries, felstone,quartz rock

,quartz , greyw acke, etc., and they vary in size from mere

pebbles up to blocks four and five feet in diameter. The general characterof the deposit is that of a coarse boulder conglomerate

,in which some

times all trace of bedding is lost. No metamorphic nor igneous rocksfrom w hich the boulders in thi s conglomerate could have been derived

,

exist in the neighbourhood ; nor indeed do such rocks of pre - Llandeiloage occur nearer than the Laurentian rocks of the north - w estern Highlands and islands of S cotland. Possibly the boulders m ay have comefrom some ancient Atlantis ; and considerin g the great size of many ofthe blocks, and the considerable distance they may have travelled, it is notunreasonable to conj ecture that ice may have had something to do withtheir transport. No ice -mark ings

,how ever

,w ere observed upon any of

the stones nor, when we reflect upon the vast age of this deposit , couldthese be expected to have resisted the long - continued action of percolatingwaters .9 . The general strike of the rocks of the district is N E . and S .W ., and

the strata are almost always inclined at high angles . The beds have,on

the w hole, a prevailing dip tow ards the south- east ; but immediately southof Colm onell it w ill be seen, from the Opposing dips indicated upon theMap, that the strata are in fact arranged in synclinal and anticlinalfolds. E ven when the dip is persistent for several miles towards thesouth - east, this need not imply a vast thi ckness of strata, for the bedsmay simply be throw n back upon each other in a series of rapid folds

,

the tops of the arches or curves having been removed by denudation.Thus the same beds may again and again appear. S ome magnificentexamples of contorted strata occur in the bold sea- cliffs between Dow nahPoin t a nd F innart Bay . In some places the greyw ackes are curiouslyhoneycombed with circular and oval cavities

,the origin of which does

not appear evident. They may perhaps denote the former presence ofsomething organic. Ripple marks have been observed upon the surfacesof some of the fin e- grained greywackes, but they are not very common.10. The S ilurian strata of the di strict, as in dicated on the Map, are

traversed by dykes or veins of in trusive rocks. These generally ru nalong the prevalent line of strike, and present much the same petrographical characters as the similar intrusive rocks w hich are m et w i th in theS ilurian uplands of the south of S cotland. The most common variety isa pin ki sh, fin ely crystalline or compact felstone, porphyritic with crystalsof felspar, and sometim es containin g clear quartz in globules scatteredthrou gh the m atrix. Dykes of dark - coloured diorite also traverse theS ilurian strata in some places they coin cide in direction w ith the felstonedykes just described, and must be distin gui shed carefully from the laterset of dolerite dykes

,to be afterw ards referred to.

b. District North of th e S t in ch a r Va lley .

1 1 . Betw een the two S ilurian districts w hich are divided by the line ofthe S tin char valley, there is as much diversity in geological structure as

9

there is in external outline . To the north of that valley the Silurian rocksappear to belong almost entirely to the Caradoc group, though some portions south of Girvan may perhaps be referable to the Low er Llandoverygroup . The structure of the ground, however, is exceedin gly complicated ,and cann ot be adequately described, w ithout taking in the district to theeast

, w hich will be elucidated in the explanation to Sheet 8. Over andabove their foldings and fractures, the rocks have been to a large extent,and over a considerable area

,metamorphosed.

1 2 . Where the metamorphism and the intruded crystalline rocks areabsent, the strata are found to consist of greyw acke, shale, conglomerate,and limestone . Of these the limestone is the most important member,inasmuch as it contain s fossils, from w hich the Caradoc horiz on of thestrata is determined. It is a w hite or grey compact amorphous rock

,

occurring in large lenticular masses,and usually associated w ith coarse

conglomerates,w hich sometimes both un derlie and overlie it. It is well

exposed in the large quarries at Aldons smaller portions occur at LittleL etterpin and Pin m a cher. E ast of these localities, it forms large massesbetw een the valleys of the Assel and S tin char. In the metamorphictracts also a number of exposures of limestone have been noted

,as

shown upon the Map. Though surro unded n ow by more or less crystalline altered rocks, there can be no doubt that these latter areas oflimestone, as shown by their fossils, belong to the same series as thelimestones to the north- east .

1 3 . Fossilsfrom theL imeston e a t Aldon sfi‘

Cytheropsis Alden sis. Tu rbosp . Mu rchison ia large sp. n ew .Ma clurea Loga n i . Holopea ?

m ag n a . Bellerophon .Raph istom a

?

1 4. The conglomerates form a very marked feature among the Caradocrocks of this region. They give rise to bold craggy hills

,of w hich ex

amples are furni shed by the Din vin Hill, Glen drissock Hill, and the Byne

Hill ; or, w hen in smaller mass, they stand out as a rough top to a smoothsloped eminence,— as in the Dow Hill, to the south of Girvan. % suallythey are very coarse in texture, their well- rounded stones consistin g ofsyenite, quartz , porphyry, felstone, greywacke, serpentine, etc. As a rule,bedding is either absent

,or can only be indistin ctly made ou t . Where

,

how ever,the stones are sm aller in siz e

,the conglomerates become distinctly

bedded,and pass off into mere pebbly grits. The matrix varies in colour

from a dirty brow n to a dull green,the latter being the prevailing colour

to the east of the present Map . In texture the paste is sometimescoarse and granular, sometim es fin e- grained ; and occasionally so hard,that, as in the Byne Hill, the smooth casts of the stones are preserved init long after the stones themselves have fallen out.15. In

'

the area embraced by the present Map,the only locality w here

a contin uous intelligible section can be followed for some di stance,is along

the coast- line between Girvan and Kennedy’s Pass . On the beach atSha lloch, beds of very coarse conglomerate, greyw acke, and shale arefound dipping to N.E ., or standing on edge, and much contorted . A littlefarther south, beyond these disturbed strata, a series of beds begins atSha lloch Mill, and, striking south- w estward nearly parallel w ith the coastline

,extends as far as the foot of Pin ba n eHill, where the metamorphosed

rocks commence. Along the beach from Sha lloch Mill to Ardw ell Bay,

the dip is at high angles to S .E . ; on the inland slopes behin d Ard

See the list from the Craighead lim eston e, in E xpla n ation of Sheet 1 4 of theGeological Su rveyMap , par . 1 4.

10

millan , and thence along the shore to Kennedy’s Pass

,the dip is north

westward. Hence it w ould appea r that the rocks here are di sposed ina synclinal trough

,the axis

'

oi w hi ch runs through Ardw ell Bay. Alongthe south- eastern edge of this trough

,a massive conglomerate rises from

under the other beds,a nd stretches southw ards until lost among the meta

morphic rocks . Here a n d there,too

,on the points of the farthest pro

m on tories,we fin d coarse conglomerate and pebbly grits rising from under

the beds on the other side of the syncline. Above these low er strata thereare exposed on the beach

,beds of hard greywacke

,shale

,and pebbly grit.

One zone of red and green shale is particularly observable. Throughoutthese beds

,courses of nodular impure limestone, or cement- stone, fre

quently occu r,and sometimes contain w ell- preserved fossils. The manner

in which the beds are broken and twisted by small faults,can be readily

examin ed on the beach,where also the numerous dolerite dykes, to be

afterw ards referred to,are well di splayed. The shore to the south- west

of Ardw ell is occupied by a series of hard fla gston es and fla ggy shales,which are either vertical

,or inclin ed at steep angles to NW . They are

frequently much tw isted and broken, more particularly as they pass southwestw ards . They lie directly upon the conglomerate of Kenn edy’s Pass .To the south of Ardmillan House

,how ever

,close to the northern margin

of the conglomerate, certain beds of shale and greywacke were detectedby the Geological Survey, from w hich a large sui te of fossils w a s obtained.

1 6 . F ossils Collectedby the Geologica l S u rvey a t Ardm illa n B ra e.

S ten opora fibrosa . Modiolopsis or Am bon ychia .Heliopora (Favosites). Orth on ot a .Petra ia elon ga ta .

Holopell a ? sp.I llaen u s Bowm a n n i. Holopea .Asaphu s giga s Raph istom a len t icu laris.S tygm a 1a tifron s . sp .

S tau roceph alu s globiceps. Mu rch ison ia .Phacops Brogn iart i . Ma clu rea .

Da lm a n n i . Cyclon em a crebristria .

Bron teu s Hibern icu s . Ophileta com pa cta .

Orthis eleg an tu l a . Con u laria elon ga ta .ca lligram m a . Theca 1 eversa .

v ar. v irgata . tria n gu l

s .p v ag in a la .

Rhy n chon ell a (Retzia ) cu n ea ta . sp .Leptaen a ten u i cin cta . E ccu l iom ph a lu s m in or.

se1 icea .*

sp.

Strophom en a gra n di s.a ren a cea . Bellerophon a cu tu s .

Discin a laev ig a ta carin a tu s.triloba tu s .

Cu cu llella or Area . Orthocera s im bricatum .Cten odon ta . ibex.Modiolopsis. sp.Species m arkedw ith asterisks areparticularly abu n da n t a t this locality.

1 7 . The metamorphic rocks of th is district, although numerous andvaried in character

,may yet be conven iently grouped into three classes

— Felspathic Rocks, Diorites, and S erpentines . These m asses usually

occu 1 in belts or bands, agreeing i n general dip and strike wi th thesurroundin g u naltered strata. The chief interest which is attachedto the altered strata of this district consists in the fact that they exhibitcertain arrested stages of metamorphic action, so that we can in manyinstances begin with unaltered beds, and trace their gradual passage

1 1

into crystalline rocks,which cannot be distinguished from those which

have had a true igneous origin. The Felsp a tlzz'

c roe/cs are by far themost abundant

,and vary much in structu re and aspect. A common

character among them is that of a dull,compact, sparingly por

phyritic rock, a n d much resembling many of the true porphyrites ofthe Old Red S andstone. The more crystalline rocks belonging to thisdivision are in dicated in the Map by a dark tint, and lettered F— thepale shade of carmin e

,lettered '6 , representing those portions of the

strata w hich are less crystalline, and in w hich the original character o fthe strata may not unfrequently be observed. The D z

'

orz'

tes and Serpentin es have a more definite character than the last mentioned group ofrocks

,and are often in terbedded, or very closely associated. The former

(Diorites) are expressed in the Map by the dark shade of carmine, w ith %white stipplin g, while the Serpentin es are marked out by green wavylines on a pale carmine ground. A glance at the Map w ill show that allthese rocks stretch across the district in a series of alternate bands fromsouth- w est to north - east

,thus corresponding w ith the general strike of

the S ilurian strata. Their northern boundary w ill also be seen to beexceedin gly irregular, portions of the crystalline masses stretchin g outinto the unaltered strata, w hi le faults and overlaps of OldRed Sandstoneadd still more to the confusion. The detailed structure of this interestin gregion w ill be described in the Geological Survey’s rlfem oir on the Geologyof Ayrshire. The follow ing table of the more im portant rocks, and thelocalities where they are best seen

,may in the meantime be of service

a . Felsp a th i c R ock s .

1 . Am ygda lmda l . Localities .a . Gra n u l ar strata , w ith scat Betw een Balcreu ch a n Port a n dPort Vad.

teredpa tches havin g a vesicu l a r stru ctu re.

b. Am orphou s, dirty - green a n d Between Ba lcreu ch a n Port a n dPort Vad.brow n rocks, w ith bom bl ike patches of am ygda loid.

Am ygda loid, w ith spherica l Coast betw een Kn ockgow a n Hill a n dthecavi t ies . m ou th of the S tin ch ar ; a lso a t m a n y

poin ts on the shore n orth of Ben n a n eHead.

2 . Felspar Porphyl‘

y. Shore, foot ofBa lcreu cha n Burn Kn ockgow an Hill ; etc.

3 . Brecciform Rocks. Shore n ear Ben n a n e Head, Kn ockdolia nMany of these are alteredconglomerates .

4. F inely - crystalline Rocks . Vatl

l

pou

j parts of shore n orth of Ben n a n e

ea

b. D iorit ic R ock s .

1 , Diorite. Balsalloch , Carleton , Len da lfoot, FellHill , etc.

2 . Syenite. Byn e 11111, Ailsa Cra ig .3 . Hypersthenite. Shore at Len dalfoot.4 . Diallage Rock , Shore a t Len da lfoot.

c . S erpen t in e, etc .

1 . Serpentin e . Shore a t Len da lfoot ; Balh am ie Hill ;hill s from Len da lfoot to theByn eHill .

2 , Altered Limestone , Shore n ear Pin ha n e, L a ifin cleary Whilk ;Ben n a n e Head; Kn ockdolia n Hill ;Often very serpen tm ou s. Kn ockdolia n Bridge; etc .

1 2

18. Ailsa Craig is an oval- shaped island, lying ten m iles west fromGirvan. I ts extreme height is 1 1 1 3 feet, its longer (or N. and S .) diameter is about 1500yards, and its shorter (or E . and W.) diameter, from1000to 1 250yards. I t rises n early vertically from the sea

,on all sides

except the east. There a triangular patch of low shingly ground in tervenes betw een the base of the steep eastern declivity of the island and thewaves . The Craig consists of a grey fin e- grained syen i te

,which

,on the

southern and western precipices,show s a system of close, parall el, vertical

joints, by w hich a. columnar aspect is given to the rock. Though noS ilurian strata are visible here, there is every reason to believe that thissyenitic mass rises among rocks of that age

,resembling in thi s respect

,

as well as to some extent also in petrographical character,some of the

crystalline rocks which rise through the S ilurian strata of the south ofAyrshire. Dykes of dolerite run in a north- westerly direction throughthe syen i te. These belong to the late series referred to in par. 2 1 . On eof the most interesting features on Ailsa Craig is seen in its parallel linesof shingle

,marking successive stages in the advance of the coast. (See

par .

Old Red S an dston e.

1 9 . Tw o areas of red sandstone and conglomerate are marked uponthi s Map. One of these is cut through y the lower reaches of the GirvanWater

,and forms a continuation of the Middle Old Red S an dstones

which stretch northwards to near the Heads of Ayr, a n dea stwards to

Maybole and the Doon. These strata are more fully described in theE xplanations of Sheets 1 3 and 1 4. The second area lies a s a small cu tlier in the valley of the Byn ehill Burn, a little to the south of Girvan.That this outlier belongs to the Middle Old Red Sandstone series isin ferred both from its proximity to the members of that series

,so well

seen on the hills to the sou th'

of the Girvan Valley, and thence northw ardto near the mouth of the Doon, and from the similarity of its beds to thoseof these adjoining tract s. As indicated on theMap, the existence of theoutlier has been largely determined by a series of faults

,by which the

newer strata havebeen throw n in among the S ilurian rocks . On thesouthern margin of the outlier, however, we meet with its lowest beds,lying unconformably upon and made up from the waste of the olderformation. These bottom strata dip, on the whole, in a more or lessnortherly direction, and this continues to be the prevalent inclinationthroughout the length of the outlier. The an glevaries from 5

° up toor even to The strata consist chiefly of dark red sandstones

,some

times passing into a dirty - green tint. Along with these,there occur

several thick zones of conglomerate, w hich, in its higher beds, is reddishin colour

,and cons ists chiefly of different fragmen ts of redgreywacke.

Tow ards the base of the series, however, the tint becomes greenish andas these conglomerates have been derived from the older S ilurian conglomerates

,they are sometimes hardly distinguishable from the latter

,

more especially where they have been thrown into a vertical position.

I n the stream between the tw o farms of Drum fairn and Ca irn top, conglomerate is seen resting upon and made up of the green serpentinerock of the metamorphi c Lower S ilurian series. The metamorphism

,

therefore, is here older than a part of the Middle (i ) Old Red S andstone.I n the Byne Hill Burn , from the farm ofBa lkea chy to Byne Hill Bridge,and also in several of its tributaries between these two points

,excellent

sections of the san dstones and cong lomerates areexposed.

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region which stretches from Nithsdale to Loch Ryan and Luce Bay. I tshills and valleys diverge from high groun ds w hich served as an in dependent centre of dispersion for the ice of at least the later stages of theglacial epoch . Hence the markings w hich have been left upon its rocksbear witness to themovement of thick masses of ice from these high groundsoutwards into the I rish Channel. In the valleys they run along the hillsides, indicatin g that the valleys served formerly to drain off the ice asthey now drain off the water. But that the ice was in mass sufficient notonly to fill the valleys

,but to moun t over the intervening ridges

,is well

shown on the range of hilly ground betw een the S tin char and the Girvan.There the striae on the rocks look directly up to the great Gall oway uplands . The knolls have still the characteristic forms of roches m ou ton n e

’

es,

even where the striae have been effaced by time. Thi s is adm irably seenin the hollow of the ridge between the F ell and Byne Hi lls aboveArdmillan House, where the well ice- worn hummocks of diorite still retain in places their striae pointing to W . 5

° N. Where the coast - line islow , the StI

'lEB on the ro cks retain the direction with w hich they have adv a n ced from the interior . This is well shown on the beach at Sha llochMill, w here, under a recently removed covering of boulder clay, the fin egrey S ilurian shales retain the ice - groovin gs whi ch strike W . 5

° N.When

,how ever

,the ground rises more steeply from the sea

,the trend of

the striae corresponds, on the whole, with that of the coast - line. E xamples of this relation are seen on the flanks of Pin ba n eHill, at Dow n a nPoint

,and a little south of the shore end of the S tin char fault. From

these facts it appears that the low ground n ow covered by the F irth ofClyde w a s fil led w ith ice moving steadily southw ard, and that into thi smain sheet there flowed thick masses w hich descended along the valleysfrom the high lands o f Carrick and Galloway.2 5. The Drift of thi s hilly district presents many features of interestwhich cannot properly be described without reference to the ground tothe east (Sheet There are two boulder clays, a lower and an upperdeposit. The lower boulder clay, usually concealed below the overlyingdr ift

,is for the most part only to be seen in stream cuttings w hen these

go deep enough. Its usual character is that of a stiff, tenacious, lightbrown

,and sometim es greenish- grey clay, thickly set w ith numerous well

striated and polished stones . These have been exclusively derived fromthe rock s of the district. Between this deposit and the upper boulderclay

,beds of earthy gravel and sand occasionally occur. The upper

boulder clay is generally of a dirty- brownish colour. The stones withwhich it is charged

,although often well scratched and smoothed, yet, as a

rule, are larger, more angular, and less polished than the correspondingstones in the low er deposit . It is frequently rudely stratified, containinggravel a n d sand

,and guttapercha clays in places . E ven where such

intercalated beds are absent,lines of ston es can frequently be traced.

Many large boulders occu r,in this drift, w hich often appear to pass into

a coarse shin gle and boulder gravel, closely resembling moraine matter incharacter. This latter kind of drift is abundantly scattered over the hillygrounds south of the Stin char valley, where it is occasionally heaped upin to moun ds . I t is in the valleys where the stratified character of theupper drift is most apparent . A fin e section of stratified upper boulderdrift is seen in the old sea cliffs n ear Benn ane Head, where the sandybeds have yielded comminuted fragments of shells.2 6 . Kames of sand and gravel have been observed a little north of

Kn ockdolia n Hill ; mounds of coarse gravel and angular d%bris also o ccurhere and there along the northern flank of the Au chen crosh Hills. Thesemounds

,and probably the kames at Kn ockdolia n also, appear to be con

h ooted with the upper boulder clay. The drift generally lies thickest

15

in the valleys, appearing only in a sparse and scattered mann er uponthe hill- tops, w here, however, it often attains a considerable thi ckness,especially in the hilly region south of the Stin cha r.2 7. E rratic blocks are very numerous, and often attain a great size .

Several very large boulders of greywacke and other Silur ian rocks occurat Pyell Craig, on the north bank of the S tin cha r between Ballantrae andColmonell . One of these, called the Cloven Craig

’

(formin g one of astream of boulders), is a great mass split along the j oints in to three mainfragments . The largest fragment must contain upwards of 2 500cubicfeet

, a n dthe other tw o portions are not much smaller. Granite bouldersbrought from the mou ntains round Loch Doon abound. They are particu la rly numerous in the valley of the Girvan, and on the beach north ofthe mouth. of that stream.

R aised Beach es .

28 . Traces of old coast - lines at a higher level than the well-marked25- feet raised beach are seen at Girvan and Ballantrae ; at the latter placetw o such higher terraces are seen, the low er being 50feet, and the higher75 feet above the sea. On the side of Dow n a n Hil l, at the mouth of theS tin cha r, several high- level ledges have been excavated on the slope ; butthese are on ly seen w hen looked at from some little di stance. Thehighest of these ledges is about 300feet above the sea. The rocks are

,

however,so much broken up and weathered

,that the terraces

,on a closer

inspection , can hardly be traced . They are best seen from a point alittle w ay up the valley of the S tin cha r.2 9 . On the north side of the Girvan, a li ttle above its mouth, there aretraces of a terrace w hich may represent the 40- feet beach of the w est ofS cotland. Fragments of w ha t seems to be the same terrace are foundfarther south, near Sha lloch Mill, a n dat Ardmill an.30. The 25- feet raised beach forms one of the most marked features ofthe coast scenery of this district. F rom Girvan to Ballantrae it runsalong the coast - lin e as a narrow strip of flat meadow land, from theinn er margin of which, representin g the former coast - line, the hills riseabruptly in to the interior . This terrace has here usually been cut outof boulder clay, as is w ell seen at Girvan, and thence southwards toKen nedy’s Pass, at Lendalfoot and Ballantrae ; in other parts of itscourse it has been excavated in solid rock. At one or tw o placesbetw een Girvan and Ball antrae the terrace is in terrupted by the advanceof the high grounds into the sea. At Benn ane Head

,for example

,an

in terruption of this kind takes place,but the beach immediately recom

menees on the other side.

Blow n S an d, Sh in gle Beach es .

3 1 . Patches of blow n sand occur at Girvan,Lendalfoot, and Ballantrae.

These have to some extent spread over and heightened the 25- feet raisedbeach, as has lik ew ise happened along the rest of the Ayrshire coast- lineto the north . They form mounds and ridges

,which are covered over

with coarse grass, and eventually converted into pasture land.3 2 . At the mouth of the Stin char no blown sand is formed

, asthe

whole flat there is liable to be flooded by the river after unusually heavyrains . It may be mentioned here, that, since the publi cation of theOrdn ance Survey Map, in 1 859 , the Stin cha r has opened for itself a n ewmou th through the high gravel bar which at this poin t stretches alongthe coast, the old mouth being n ow closed.3 3 . On the east side of Ailsa Craig a low triangular piece of groundlies at the base of the cliffs . This consists of coarse shingle

,which has

LI ST P% BLICATIONS

OF THE

GEOLOGICAL S% RVE % OF SCOTLAND.

I .—Maps on On e- in ch S ca le.7 . Ayrshire, S outh-Western Districts . 63 .1 3 . Ayrshire, Turnberry Poin t. 43 .14. Ayrshire, S outhern Districts . 63 .24. Peeblesshire. 6 3 .3 2 . E dinburghshire and Linlithgowshire. 6s.3 3 . Haddingtonshire. 63 . if

3 4. E astern Berwickshire. 4s.40. Fife a n dKin ross. 63 .41 . Fife, E ast part. 63 .

I I .—Maps on S ix- i n ch S ca le, illu stra tin g th e Coa l -fields .E din burghshire. Sheets 3 , 8 , 1 4, 1 7. 43 ,

Sheets 2 , 6 , 7, 1 2 , 1 3 , 1 8 . 63 .Haddin gton shire. Sheets 8, 1 3 . 43 .

Sheets 9, 14. 63 .Sheets 3 3 , 3 7. 43 .Sheets 24

,25, 30, 3 1 , 3 2 , 3 5, 3 6. 6s.

Ayrshire. S heets 2 6, 3 1 . 48 .Sheets 1 9, 2 7, 2 8, 30, 3 3 , 3 4, 3 6 4050. 68.

HI .—Hori z on ta l S ection s . 58 . per S heet.Sheet 1 . E dinburghshire and Haddin gtonshire.

2 . E dinburghshire and Haddingtonshire.3 . Peeblesshire, E dinbu rghshire, Linlithgowshire.

I V.—Vert ic a l Section s . 3 3 . 6d. per S heet.

Sheet 1 . E dinburgh Coal- field.

V.—Gfiologica1Mem oirs, to a ccom pa n y th e Sheets of th e On e- in chap .

Sheet 7. Ayrsh ire, S outh-Western District. 3 d.1 3 . Ayrshire, Tu rnberry Point. 3 d.14. Ayrshire, S outhern District. 3 d.24. Peeblesshire. 3d.3 2 . E dinbu rghshire and Linlithgow shire. 48. I n cloth boa rds, 58.3 3 . Haddingtonshire. 2 s.3 4. E astern Berwi ckshire. 2s.

A Deta iled Cata logue m ay be had gra tis, on am lz'

ea tz'

on to the Geologica l Su rveyOfice, E dinburgh, or toMessrs W. drA.K. John ston , 4 S t An drew

Agen ts appoin tedfor the Sale of thePubli ca ti on s of theGeologica l Su rvey.

L ondon —Messrs L n 'r'rs SON, Royal E xchan g e, E .C. ; Messrs LONGMAN, Patern oster Row ; Mr STANFORD, 6 Charing Cross, W .C. ; Mr W% LD, 1 1 a nd1 2Charin g Cross.

E din bu rgh—Messrs JOHNSTON, 4 St Andrew Square.

Dublin —Messrs HODGE s Smrm . 104 Grafton Street.