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THE BACKBENDER'S GAZETTE AUGUST 2007

remarkable nature of the concretions comprising Rock City.

Schoewe (1937) and Schoewe et al. (1937) recommended that Rock City be recog-

nized as a National Monument. On May 29, 1977, Rock City was dedicated as a

National Natural Landmark. It was the third National Natural Landmark to be created

within Kansas.

Physical Character

Rock City consists of

about 200 concre-

tions which occur as

three distinct clusters

within an east-west

belt about 1640 feet

(500 meters) long

and 130 feet (40

meters) wide. The

central cluster is the

largest and best pre-

served of these clus-

ters. It contains about

84 concretions which

are generally about 90

percent exposed.

They rest on low ped-

estals of host sand-

stone which often ex-

hibits Leisegang

banding and contains

abundant pea-size and

grape-size carbonate concretions. The 52 concretions of the east cluster are almost as

well preserved as those in the central cluster. The 70 concretions forming the west

cluster are more weathered, buried, and fragmented than those in the other clusters

(Schoewe 1937, Ward 1938, McBride and Milliken 2006).

The concretions which comprise Rock City vary greatly in size and shape. These

concretions exhibit a wide variety of spherical, subspherical, loaf, and irregular shapes

(Figures 1 and 2). Some of them have truncated tops. In terms of size, they typically

range in diameter from 10 to 20 feet (3 to 6 m) with an average diameter of 11.8 feet

(3.6 m). In the central cluster, concretions have coalesced to form a loaf-shaped com-

pound concretion, which is 27 feet (8.2 m) long and 8 feet (2.4 m) high (Schoewe

1937, Shafer 1937, McBride and Milliken 2006).

These concretions consist of well-sorted, medium-grained sandstone which are tightly

cemented by poikilotopic and displacive fibrous calcite. The sand fraction consists ofabout 95 percent detrital quartz. The remainder of the grains consist of chert, mica-

ceous metamorphic, rock fragments, muscovite, heavy minerals, and intraclasts. Par-

Figure 1: Typical view of concretions within thecentral cluster of Rock City. Photograph courtesy ofKansas Geological Survey from Photos from OttawaCounty Web page, which is accessed from

http://www.kgs.ku.edu/Images/DB/index.html.

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zoic, Geology. unknown publisher, New York, New York, 624 p.

Chamberlin, T.C., and R.D. Salisbury. 1914. Introductory Geology. publisher unknown,

New York, New York, 708 p.

Folk, R.L. 1968. Petrology of Sedimentary Rocks. Hemphill Publishing Company,

Austin, Texas, 182 p.

Forsyth, P.J., and G. Coates. 1992. The Moeraki boulders. Information Series no. 1,

Institute of Geological & Nuclear Sciences, Lower Hutt, New Zealand, 6 pp.

Franks, P.C., G.L. Coleman, N. Plummer, and W.K. Hamblin. 1959. Cross-stratifica-

tion, Dakota Sandstone (Cretaceous), Ottawa Couty, Kansas. State Geological Survey

of Kansas Bulletin, no. 134, part 6, pp. 223238.

Gould, C.N. 1901. The Dakota Cretaceous of Kansas and Nebraska. Kansas Academy

of Science, v. 17, pp. 122178.

Hay, R. 1893. Geology and Mineralogy Resources of Kansas. State Board of Agricul-

ture Biennial Report 1891-1892, v. 8, part 2, pp. 99162.

Landes, K.K. 1935. Scenic Kansas, State Geological Survey of Kansas Bulletin. no.

36, 55 p.

Mack, L.E. 1962. Geology and ground-water resources of Ottawa County, Kansas.

State Geological Survey of Kansas Bulletin. no. 154, 145 p.

McBride, E.F., and K.L. Milliken. 2006. Giant calcite-cemented concretions, DakotaFormation, central Kansas, USA. Sedimentology, v. 53, no. 5, pp. 11611179.

Mudge, B.F. 1878. Geology of Kansas. State Board of Agriculture Biennial Report, v.

1, pp. 4688.

Schoewe, W. H. 1937. The Geology of Rock City. Transactions of the Kansas Acad-

emy of Science, v. 40, pp. 180191.

Schoewe, W.H., W.H. Horr, C.E. Burt, and L.D. Wooster. 1937. Symposium on the

geology, flora, and fauna of Rock City, a proposed national monument in OttawaCounty, Kansas. Transactions of the Kansas Academy of Science, v. 40, pp. 179180.

Shaffer, H.L. 1937. Concretions in the Dakota Sandstone. Compass, v. 17, p. 87-90.

Simpich, F. 1937. Speaking of Kansas. National Geographic Magazine, Aug. 1937,

pp. 135182.

Thyne, G.D., and J.R. Boles. 1989. Isotopic evidence for origin of the Moeraki septarian

concretions, New Zealand. Journal of Sedimentary Petrology, v. 59, no. 2, p. 272

279.

Ward, H.K. 1938. Concretions of Rock City. Mineralogist, v. 6, no. 6, pp. 2324.

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Volume XXXVIII - No. 8 August 2007

The Newsletter of theHouston Gem & Mineral Society

Houston, TX

Continued on page 4

General Meeting Programs

Presidents Message

by Matt Dillon

J

uly is here, and the hot weather I have been

talking about is coming along with it. How

ever, June and July brought us more rain than

normal, so some of our activities had to be put off

or plans changed as a result. Some of this rain fell

in south and southwest Texas, and I am sure those

of you venturing out this fall will find that erosion

from all the rain improved your chances of finding

good material.

Our Show Committee is working hard preparing for our annual show in Humble,

September 2123, 2007. Those of you wishing to help should contact our Show Chair-person Sigrid Stewart or her assistant, Michele Marsel. They have initiated a New

Volunteer Incentive Program which involves earning a Show Buck for every shift

you workanother good reason for helping out.

In addition, Scott Singleton is busy planning our hosting of the 2008 American Fed-

eration of Mineralogical Societies Annual Convention during our 2008 show.

Changes are taking place around our clubhouse, and you no doubt have noticed much

progress on the new room being built in the large open storage area. Tom Wright,

David Hawkins, Wayne Barnett, and many others have put in hours of hard workduring this project which still has a way to go. You may also notice that the parking

lot is restriped with a fresh coat of yellow, and we will also paint the concrete blocks

July 24: Kazakhstan Metal Work--Our own Neal Immega will speak on the spec-

tacular metal work to be seen in the Kazakhstan exhibit currently on display at the

Houston Museum of Natural Science. Neal is a docent at the HMNS, and he may be

able to arrange for a low cost or free tour of the exhibit for interested members on aSaturday or Sunday.

August 28: To be announced