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Miner illogical characters. These beds are often a slightly 
argillaceous yellowish sand, in which the fossils are imbedded 
without cohesion. In other instances the matrix is hard and 
siliceous, obviously composed of fine sand. In others, again, 
a yellowish or gray clay forms the strata, and sometimes all 
these substances are variously mixed, but the lower stratum is 
invariably a lead coloured clay or argillaceous marl. There is 
mostly some intermixture of comminuted shells, but that the 
fossils of these beds have been deposited in a tranquil sea, is 
obvious from the extreme perfection of the shells, and the con- 
stant occurrence of the most delicate bivalves, with both valves 
in their natural connexion. 
Organic characters. Speaking of this formation, in Europe, 
Conybeare and Phillips remark, that “the shells are found in an 
excellent state of preservation, and though generally in a con- 
fused mixture, are sometimes so disposed, that patches of par- 
ticular genera and species appear.” 
“ Like fossils of most other strata, this assemblage of shells 
manifests a peculiar distinctive character. A few shells only, 
which may be placed among those which are supposed to be 
lost, or among those which are the inhabitants of the distant 
seas, are here discoverable, the greater part not appearing to 
differ specifically, as far as their altered state will allow 7 of de- 
termining, from the recent shells of neighbouring seas.” 
The above description is strikingly applicable to the American 
Upper Marine beds, in certain districts, but in others a large pro- 
portion of extinct species, and such as inhabit distant seas, are 
of common occurance, and manifest a difference in the relative 
ages of the deposits, yet none of those w hich I am now consid- 
ering exhibit any of the characters peculiar to the London clay 
and Calcaire grossier. For the present, it may suffice to re- 
mark, that of all the species which these strata have hitherto af- 
forded, about forty are specifically identical with the living 
Testacea now inhabiting the coasts of the United States and 
the islands of the West Indies. A considerable number of spe- 
cies are common to the strata of Europe and America; while 
some of these very shells are also found recent on both sides 
of the Atlantic, shewing how extensive may be the distribution, 
and how long the duration of a single species. 
Geographical distribution. This formation first appears in 
