Adrinées before thé-Association-ef-Aindtioan Geologists. 248 
in the western part of Pennsylvania and New York; and this 
opinion becomes more probable, since the discovery by Mr. Con- 
rad, of remains of the Holoptychus nobilissimus, a fish very char- 
acteristic of the old red sandstone in Great Britain. Mr. Hall 
makes this group four hundred feet thick, lying immediately 
beneath the coal measures. 
‘Strong reasons have been presented by Messrs. Conrad and Va- 
nuxem, founded upon a comparison of organic remains, for suppo- 
sing that a large part of the rocks below the old red sandstone, in 
the vast area under consideration, and especially in New York, are 
identical with the Silurian rocks of Great Britain. The former 
gentleman recognizes all the important subdivisions of this group 
described by Mr. Murchison, except perhaps the Llandeilo rocks, 
which are the lowest.. The Caradoc sandstone, the Wenlock 
shale and limestone, and the Ludlow rocks, are distinctly mark- 
ed.* And in speaking of organi aius, as a means of identi- 
fying strata, he remarks, that “an instance never occurs in this 
country, where the species of ont formatic are continued into 
dispute regarding its geological age. » All the various eras are ad- 
mirably recorded, each by its peculiar group of animal or vegeta- 
ble remains; and to him who has carefully studied them, they 
are quite as intelligible as if the hand of nature had arranged 
them in a cabinet for his use.”—Am. Journal of Science, Vol. 
35, Pp. 237. : yo 
These suggestions open a wide field for investigation. It is 
one of the most important problems in American geology ;—and 
from the immense extent occupied by these rocks, I can hardly 
doubt that here will be found the most complete type of the tran- 
sition formations that has yet been deseribed. Accordingly, in 
his report for 1841, Mr. Conrad ‘says, that “ nature has probably 
enabled the geologist to apply this classification (of Murchison ) 
in a-more-clear and satisfactory manner to the rocks of this coun- 
try than to those of Europe, since the series is certainly more 
ete, and the organic remains more abundant in species.” [ 
He says: «the inhabitants of the ‘seas (in which these rocks were de- 
ee a corse Pe : ded, at five different epochs; 
and one of these groups is no more to be compared with another, than the oolite 
wee 
