Association of American Geologists and Naturalists. 149 



ment of highly curious generalizations, in relation to the limits of these 

 extinct races, and the conditions which have controlled their distribution. 



Guided by the ascertained boundaries of the principal groups of 

 fossils, and also influenced by the great natural lithological horizons, 

 the geologists in the diiferent quarters of the wide Appalachian field 

 have sedulously aimed at making such an analysis and classification 

 of the strata as would best accord with the special type which they 

 present in their respective district. Seeking at first for a classification 

 founded on local and not general characteristics, the subdivisions hith- 

 erto instituted only admit of extension to districts beyond those for 

 which they were framed, in so far, as the strata retain with more than 

 usual constancy these local features. Hence a general scheme of 

 grouping, applicable, if possible, to the whole region occupied by the 

 strata, and expressed in terms significant of general and not local and 

 restricted relations, is yet to be supplied. 



The most elaborate classification of our Appalachian palaeozoic 

 strata, hitherto published, is that of the New York geological survey. 

 From the very considerable amount of palasontological research con- 

 nected with this survey, from the diversity of formations in the State, 

 and the clear typical characters which some of them possess, this clas- 

 sification merits much attention. It embraces under the title of the 

 New York system, the entire body of strata from the bottom of the 

 lowest fossiliferous rocks, to the base of the red sandstones of the 

 Catskill Mountains, the whole having in their maximum expansion a 

 thickness of about six thousand feet. This large mineral mass has 

 been subdivided by the gentlemen of the New York survey in con- 

 formity, chiefly, to the horizons established by organic remains into 

 twenty eight special formations, or subordinate masses, and these twenty 

 eight are thrown into four series or divisions named from the districts 

 where they are best developed. Observing the ascending order, these 

 are the Champlain division, the Ontario division, the Helderberg divi- 

 sion, and the Erie division. Referring you to the ample and well illus- 

 trated volumes on the geology of New York, for the views which have 

 induced the gentlemen of that survey to adopt the above classification 

 and nomenclature of the rocks, and for many valuable details connected 

 with the organic remains, I will embrace this opportunity to bring to 

 your attention some points of general interest to American geology, 

 which the perusal of these works suggests. 



In geological, as in all archseological research, the earliest periods 

 seem most to enlist our attention. Ascending the stream of time, the 



