50) PALEOZOIC PALEONTOLOGY. 
extending southwestwardly along the Appalachians, than at Trenton 
Halls, in Central New York, where the Trenton limestone was first 
deseribed. The time of the beginning of deposition of the Hudson 
River slates was previous to the close of the deposition of the typical 
‘Prenton limestone, so that the deposition of the lower portion of the 
Hudson River formation was contemporaneous with the Trenton lime- 
stone beds further west. The evidence in New Jersey of this relation- 
ship between the Hudson River and the Trenton formations is—first, 
the much less thickness of the Trenton lmestone in New Jersey, 
where, exclusive of the lower beds of Black River age, it is less than 
one hundred feet, while at Trenton Falls, New York, it is two hun- 
dred and seventy feet and at some other localities very much more ; 
and second, because the fossil faunas in the Trenton limestone of 
New Jersey, for the most part, represent only the lowest life zones 
of the formation. 
Although the age of the base of the Hudson River formation can 
be determined with some degree of certainty by the faunas of the 
subjacent Trenton limestone, the age of the top of the formation in 
New Jersey has not been determined, because of the extreme rarity 
of organic remains in the formation. The formation may be the 
time equivalent, not only of a portion of the Trenton, but also of the 
Utica and the Lorrain formations of the New York series. 
In the typical exposures of the Trenton limestone at Trenton Falls, 
New York, 270 feet have been recognized by Prosser and Cummings* 
and 268 feet by White,t but neither the bottom nor the top of the 
formation is exposed at this locality. Danaf gives the thickness of 
the Trenton limestone at Montreal as 600 feet and west of Lake 
Ontario as nearly 1,000 feet. 
- The thickness of the Utica slate, given by Dana,§ is 15 to 35 feet 
at Glen’s Falls, 250 feet in Montgomery county and 30 feet in Lewis 
county, New York. Walcott|| gives the thickness of the same forma- 
tion in its typical locality at Utica, New York, as over 600 feet. 
The Lorrain shales have a thickness of 700 feet in Scoharie county, 
New York, and a similar thickness in Western Canada according to 
Dana.§ 
* Fifteenth Ann. Rep. N. Y. State Geol., p. 626. 
} Fifty-first Ann. Rep. N. Y. State Museum, vol. I., p. 231. 
{ Man. Geol., 4th ed., p. 493. 
2 Loe. cit., p. 494. 
|| Trans. Albany Inst., vol. X., p. I. 
‘| Loe. cit., p. 494. 
