260 Address before the Association of American Geologists. 
selves in curved rather than straight lamina, and why the eurves 
should differ from one another, does not appear. ‘The siliceous 
limestone of Fontainbleau contains more sand than the caleare- 
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 lime, 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 small amount of organic matter, very prob- 
ably resulting from the crenie 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 male 
tle.” But even if we admit ‘that some soft animal formed the 
nucleus; it is impossible to doubt that the ¢laystones 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 of Kimmeridge 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 affect; although between them ale 
humerous intermediate varieties; and sometimes there would 
peter to have been a struggle between two of these forms for the 
These inant forms are the sphere, the oblate 
there, the prolate spheroid, the annulated, the lenticular, and 
the cy lindrical. The first: is the most important, though 
bien ewe Ap ego may be conceived to sm 
tom it. I think that if we may su the clay to 
pi a ake nota fluid 4 st, as to admit of “ae 
ey ee 
. wig 
