146 Cincinnati Society of Natural History. 



In short, prior to about 1820, but little was known of North Ameri- 

 can Geolog}'^ and Palaeontology, and except as a matter of historical 

 curiosity, rather than instruction, we need not seek these sciences in 

 earlier publications. 



The Mesozoic and Ctenozoic rocks, to which this essay will be confined, 

 constitute the superior one fourth part of the geological column, in 

 the sedimentary strata, of the continent; the other three fourths belong 

 to Palaeozoic age. As a striking illustration: the upturned palaeozoic 

 strata, in the little state of New Hampshire, reveal a thickness twice 

 that furnished by the Mesozoic and Csenozoic rocks throughout their 

 extensive distribution to the remotest parts of the continent. 



It will be observed in the sequel, that I have followed the chronologi- 

 cal order of discovery, as near as practicable, with a view of present- 

 ing the historj^ the development and the growth of these sciences, 

 as well as the facts, within the scope considered, upon which they are 

 now supposed to rest. 



First, we will pursue the Mesozoic rocks and fossils, and afterward 

 the Caenozoic. 



THE MESOZOIC AGE. 



The Mesozoic age is divided into three periods, beginning with the 

 earliest, as follows: 



1. The Triassic Period. 



2. The Jurassic Period. 



3. The Cretaceous Period. 



The name Triassic was given to the 1st Period in allusion to a three- 

 fold division, which it presents in Germany. The Jurassic derives its 

 name from the Jura mountains of Switzerland ; and the name Cretace- 

 ous is derived from creta, chalk. 



It will be convenient to consider the Triassic and Jurassic together, 

 because the line of separation, at many places, still remains a matter 

 of doubt, and because the rocks at one place, at one time, have been 

 considered as Triassic, and at another as Jurassic, and even now great 

 uncertainty exists as to their correct classification. 



TRIASSIC AND JURASSIC. 



In 1832, Prof Edward Hitchcock* described the New Red Sandstone 

 which extends across the State of Massachusetts, on both sides of 

 the Connecticut river. 



In 1833,* he referred all the sandstone in the valley of the Connecti- 

 cut to the age of the New Red Sandstone of Europe. The opinion was 



* Geo. of Maes. 



