Address before the Associatioti of American Geologists. 243 



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 Holoptychiis nobilissmius, 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 organic remains, as a means of identi- 

 fying strata, he remarks, that " an instance never occurs in this 

 country, where the species of one formation are continued into 

 an upper one in such numbers as to cause the least perplexity or 

 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." — .4m. Journal of Science, Vol. 

 35, p. 237. 



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 described. 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 

 complete, and the organic remains more abundant in species." I 



* He says also, that " the inhabitants of the seas (in which these rocks were de- 

 posited) have been destroyed, and new creatures succeeded, at five different epochs; 

 and one of these groups is no more to be compared with another, than is the oolite 

 with the green sand formation. "-^.6?7«. Journal of Science, Vol. 35, p. 246. 



