268 IDENTITY OF THE WESTERN FORMATIONS 



geographical names for groups or individual rocks, it is desirable 

 lo know the locality of greatest devclopoment for the whole 

 country, and when this is ascertained, the name should be adopt- 

 ed. But until the extent and comparative developement of each 

 rock is known, perfect local names cannot be prefixed ; and as a 

 step towai'd the perfection of this nomenclature, the place of 

 greatest developement in the district under consideration should 

 give the name. 



This examination westward also afforded a good opportunity 

 of testing the value of fossil characters, when applied to the same , 

 strata extending over wide ti'acts of country, and the results 

 will be seen, as we proceed, to have been mostly satisfactory. 

 The value of lithological characters at the same time was found 

 to fail in a gi*eat degree, and though in some cases persistent, yet 

 alone they would be found insufficient and often lead to errone- 

 ous conclusions. From the investigations made in New York, 

 we had learned that groups, which at orje extremity of the State 

 are of gi'eat importance and well characterized by fossils, cannot 

 be identified at the other extremity ; and the same is more em- 

 phatically true of single rocks. 



The Niagara group, so well defined by the topographical features 

 of the country, as well as by both its fossil and lithological char- 

 acters, no one has yet attempted to identify to the east of Little 

 Falls. Almost the same may be said of the Onondaga salt 

 group and the Medina sandstone ; while on going in the 

 opposite direction, we find several important members of the Hel- 

 derberg series entirely wanting west of Cayuga Lake, and the 

 Oriskany sandstone existing only in patches here and there. 



The undisturbed range of these deposits, with the gi-eat ex- 

 tent of unbroken outcrop bordering the Ontario valley and its 

 coiUinuation along the Mohawk, has enabled us to acquire a very 

 perfect knowledge of the changes in the character of strata in their 

 east and west extension. While such changes have taken place 

 in important groups, others of less apparent importance and of 

 much less thickness, are found remarkably persistent. 



In making my examinations westward, the gi'oups and individ- 

 ual rocks of New York, as adopted in the annual reports, were 

 made the basis of reference. 



