260 Address before the Association of American Geologists. 



selves in curved rather than straight laminae, and why the curves 

 should differ from one another, does not appear. The siliceous 

 limestone of Fontainbleau contains more sand than the calcare- 

 ous concretions of this country, called claystones ; and yet the 

 former assumes a polyhedral and the latter a spheroidal form. 



These claystone concretions, which abound in our diluvial 

 clays, seems to me to afford a better opportunity than any other 

 for studying this subject. They appear to consist of the clay 

 containing them, cemented by carbonate of Hme, which usually 

 forms about fifty per cent, of the mass ; although I doubt whether 

 it exists in definite proportion. I have found in them, also, both 

 in those of New England and in specimens from the diluvial 

 clay of Sweden, a sniciU amount of organic matter, very prob- 

 ably resulting from the crenic acid, which existed in the water 

 when the clay was deposited. I am informed, however, by Dr. 

 Tamnau, of Prussia, that "the Swedish scientific men believe 

 these claystones to be something of organic remains : — some 

 sort of mollusca, which were more or less wrapped in a man- 

 tle." But even if we admit that some soft animal formed the 

 nucleus, it is irnpossible to doubt that the claystones have as- 

 sumed their present forms as the result of a concretionary agen- 

 cy. Those forms are often so very regular, and furnish such 

 mimic representations of numerous artificial objects, that we need 

 not wonder they should be regarded, both in this country and in 

 England, as the work of art ; that among us, they should be im- 

 puted to the ingenuity of the aborigines; and in England, be 

 supposed to have been turned in a lathe, as a substitute for me- 

 tallic coin, and have taken the name o( Kvmmeridge coal money. 

 An examination of numerous specimens from New England, 

 has led me to the conclusion that certain predominant forms may 

 be discovered, which they aflect ; although between them are 

 numerous intermediate varieties ; and sometimes there would 

 seem to have been a struggle between two of these forms for the 

 mastery. These predominant forms are the sphere, the oblate 

 spheroid, the prolate spheroid, the annulated, the lenticular, and 

 the cylindrical. The first is the most important, though least 

 common; and perhaps all the others may be conceived to result 

 from it. I think, also, that if we may suppose the clay to have 

 been in a plastic and not a fluid state, so as to admit of the per- 

 meation of carbonate of lime in a state of solution, and that differ- 



