156 PROCEEDINGS OF THE GEOLOGICAL society. [Dec. I, 
3rdly. A series of still greater thickness m which argillaeeous 
matter is the main ingredient, and limestone very rare; the rocks 
consisting chiefly of shales and argillaceous sandstones. This series 
reaches upwards to the top of the Chemung group, and is covered 
by a red sandstone. 
The organic remains of these three great divisions are also well- 
marked, and will help us to a more close classification of the beds. 
Ist. The shells found in the lowest or Sandstone division present a 
great accordance with those found in the Lower Silurian formation of 
Europe: and in this we must include the Clinton group, notwith- 
- standing its containing a few Wenlock species, for the great majority 
of its fossils are of Lower Silurian types. 
In Mr. Lyell’s collection there are about 45 species from this 
lower series of beds, of which 14 are known European species of 
Lower Silurian age, bemg near 30 per cent. of the whole. 
Tf our Welsh specimens were in better condition and had been 
thoroughly examined, it is probable that the agreement would be 
found still greater ; but even at present it justifies the classification 
of this American series of beds with our Lower Silurian formation. 
2ndly. In the calcareous series reaching from the Niagara shales 
to the Upper Pentamerus limestone inclusive, the agreement of the 
species with ours is still more remarkable. Out of near 50 species 
in Mr. Lyell’s cabinet, 20 are European, or 40 per cent. of the whole. 
Of these European species so large a proportion belong to the Wen- 
lock period, that we must class this calcareous series with our Wen- 
lock formation. In this division we first meet some species which in 
this country belong to the carboniferous and Devonian formations, 
but they are too few to affect our conclusions. . 
3rdly. The uppermost of the three great divisions, including the 
beds from the Oriskany sandstone to the Chemung group, contains 
a great number of species, of which Mr. Lyell’s collection contains 
above 100 species; among these I can only identify 22 European 
species, being about 20 per cent. of the whole: these belong for 
the most part either to the Devonian and carboniferous systems of 
Europe, or are such species as have a wide range through the older 
formations ; with these are a very few Ludlow species: the conclusion, 
therefore, from a general examination of the fossil shells, is, that the 
beds of this division must be considered as an enormous development 
of what we have called in Europe the Devonian system. 
In the preceding arrangement of the New York series of rocks, 
no part has been classed with the Ludlow formation of this country. 
The American writers are not agreed upon this part of their series : 
Mr. Hall places the beds from the Oriskany sandstone to the corni- 
ferous limestone inclusive in the Wenlock series, with the remark 
that there are many reasons for including them in the equivalents of 
the Ludlow formation*. But as there are no species found in those 
beds which are known here as peculiar to the Ludlow formation, and 
they contain some common carboniferous species, it seems fitter to 
class them in the Devonian system with the beds above them. 
* Report on the Fourth district of New York, p. 517. 
