Remarks upon a Petrified Echinus of a Singular Kind, Shewn to the Royal Society, April 24,1755, by the Reverend Richard Pococke, LL. D. Archdeacon of Dublin, and F. R. S. Found onBunnan's-Land in the Parish of Bovingdon in Hertfordshire, Which is a Clay, and Supposed toHave Been Brought with the Chalk, Dug out of a Pit in the Field. By James Parsons, M. D.and F. R. S.Author(s): James ParsonsSource: Philosophical Transactions (1683-1775), Vol. 49 (1755 - 1756), pp. 155-156Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/104919 .

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XXVI. Remarks vpon a petrified Echinus of afingalar kird, J2ewn to the Royal Society, April 24, X 75 5, by the Reve.rend Richard Pococke, LL. D. Jrchdeacon of Dubltil, ard F. R. S. foxd on Bunrlan'sLand in tJse PariJh of Bouringdon n Hertirdthire, which is a Clay, andf>ppaHed to have been broaght with the Chalk, dug out of a Pit r the Field. ty Jamcs Parfons, M. Dw ard F. R. Ss

July 9s I755>

ReadAprillvHE mund echinites are for the I755* 1 moI} part found in chalk-pits, and

tlaey are in general, when recent, the moR tender in their Shells; fo that the chalk is the mok favour- able bed for them tcx be preferved in long enough to be petrified; whereas in other kinds of matter thefe would be mouldered and deIlroved before the pe- triScation could commence ; and it is very fingular that aImoR all thofe in tlle chalk are filled s^7ith flint, or partly chalk and partly flint, and fome- times with cryflal. Nour, as all flits and agates are nothing lefs than cryi:lal deba;fied by eartha and as it is in beds of chalk that thefe, as *vell as multitudes of larae Rones are found) one srould be aImoit illduced to believre, that chalk degeneratet

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[ IS6 ] into flint; or, in other words, that flint was produced by chalk originally. And indeed I have many fpeci- mens myl:elf, that feem to prove it; in fome of which they Seem to fhew the gradual change from the one to the other, not at all like a fudden appof1tion of chalk to flint.

Other kinds of echinites, filch as the Echini cor- dati, or heart-Shaped echinite, the pileati or conic, the galeati or helmet-ihaped, with feveral other liinds, are often formed of other fpecies of SOtly particles.

The foi1l before you, being one of the oval kind, with large papilla, is the Eehinometra digitatv /e- canda rorrnda tvel cidaris Mauri of Rumphius, which, with the other oval echinites, are very rarely found but in chalk: and it is remarkable, that whether they are filled with chalk, flint, or chryRal, their {hells break with a Selenitical appearance, juI} as the lapides Judaici, and all other fpecies of echinites found in chalk-pits, do.

XXVII.

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