POTSDAM SANDSTONE. 
This rock, with its associated slates and conglomerates, we regard as lying at the base of 
the palaeozoic strata; as having been produced at the dawning of the vital principle upon 
our planet, forming the eozoic point in our series. Nothing which bears the semblance of 
having been organic is yet known in strata of anterior origin. If, as has been supposed, 
organic forms were enveloped in the materials of the gneiss, mica and talcous slates, they 
have been so far obliterated by supervening changes that they cannot now be recognized. 
Neither has it been demonstrated, except to a very limited extent, that any of these rocks 
are of origin anterior to those which we term palaeozoic. In the metamorphosed strata of 
more recent periods, we are able to trace the gradual extinction of the outlines and substance 
of numerous organisms as we pass from the unaltered to the metamorphic condition of the 
same formations. Therefore, in strata like those of the gneiss and associated slates, where 
the present character departs so widely from what we suppose to have been their normal 
type as sedimentary rocks, we are scarcely justified in expecting to meet with organic 
remains which might give a clue to their geological age. It can only be by a thorough 
study of the structural development, that we can hope to arrive at satisfactory conclusions 
regarding the age of a large portion of the metamorphic strata on the east of our fossiliferous 
masses of the Hudson River valley.* 
* Some months since, Prof. H. D. Rogers informed me that he had discovered palaeozoic fossils in the White 
Mountain range ; and while this part of my report was passing through the press, I read the paper of Profs. H. D. 
and W. B. Rogers, “On the geological age of the White Mountains.” It would appear, from the fossils discovered, 
that these apparently ancient and highly crystalline strata are of the age of the Clinton group of New-York. Never¬ 
theless, I am, for various reasons, inclined to regard the association of fossils there mentioned, though necessarily 
obscured by igneous action, as indicating the occurrence of the Pludson River rocks, which we find extending to a 
considerable distance east of the Hudson River, charged with Lingula, Cytherina, Agnosti , and fragments of other 
Crustacea. 
I have already shown ( Transactions of the Association of Geologists and Naturalists, Ntw-Haven, May 1845), 
that the Shawangunk grits do overlie the shales of the Hudson River group in Rensselaer county, N. Y., occupying 
some deep folds of the strata beneath. The same grits and conglomerates may be seen again farther to the north in 
Vermont, capping the summits of some of the elevated ridges ; and, so far as we can discover, these coarse grits are 
conformable to the strata beneath. 
[Palaeontology.] 
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