RAYMOND: CORRELATION OF THE ORDOVICTAN STRATA. 251 



Valley, in all of which places it occupies a thin formation, its vertical 

 range never exceeding forty feet. A very few specimens have been 

 found in the lowest la vers at Trenton Falls, but it is absent from more 

 northern outcrops of the Trenton. It is not found in the Trenton 

 anywhere in the region of New York west of the Adirondacks, it is 

 absent from the Trenton of Ontario and Quebec west of ^Montreal, 

 and it is absent from ^Minnesota. The second occurrence in Xew 

 York is not in the Trenton, but in the typical Utica, at Rome and the 

 vicinity. It occurs also in the Frankfort, and still higher, in the 

 Pulaski. 



In the vicinity of Quebec the second appearance of Cryptolithus is 

 in the light-colored sandy shale about 400 feet above the top of the 

 limestone of the Trenton, and above the dark " Utica " shale. 



At Bellefonte, Penn., the earliest appearance of Cryptolithus tessel- 

 hitus is, as in New York, just above the limestone containing the 

 Leray fauna, and it reappears in the upper fifty feet of the 600 foot 

 Trenton section, at the point where the limestone begins to pass over 

 into shale, and just before the first appearance of Triarfhrus becki. 

 In Kentucky, Cryptolithus appears first in the Logana (Hermitage), 

 only a few feet above the base of the Trenton, and does not reappear 

 till the Cynthiana, just at the top of the Trenton or base of the Eden. 

 On the Ohio River at Cincinnati it is in the Cynthiana, and the Lower 

 Eden, and appears again in the Maysville. 



The occurrences are so exceedingly alike, and there is so great an 

 indifference displayed as to the character of the sediments, that I am 

 inclined to look upon Cryptolithus as an exceedingly good horizon 

 marker. If this be the case, then the Schenectady formation is to be 

 correlated with the Utica, and, probably, the Frankfort. 



CORRELATION OF THE TREXTOX IX AMERICA. 



One great obstacle to any correlation of the kind attempted in 

 this study is the fact that we have as yet reached no satisfactory 

 solution to the problems presented by our American Ordovician strata. 

 By far the best correlation tables for the Ordovician are those recently 

 presented by Drs. Ulrich and Bassler. ]My own differs radically from 

 theirs, and I am therefore compelled to traverse the principal outlines 

 of the subject in justification of the departures which I have made 

 from former schemes. 



