WILLIAM B. DWIGHT. Ome 
of quartzose and limestone rocks at the base of the 
above named mountains. 
3. The Potsdam, (or upper Cambrian, ) well exposed 
at Salt Point, and a little southeast of Poughkeepsie. 
4. The Rochdale group, (Calciferous?) This group, 
with its unique set of numerous fossils, yet only very 
partially described, is the one which in previous papers 
Thave called the Calciferous, because I considered it 
manifestly most closely related to what has been gener- 
ally covered by that title. It is evident, however, that 
the proper limits of both of the terms, Calciferous and 
Chazy, (and of course that entirely vague expression 
‘*Quebec group’’) are undergoing severe review in the 
light of recent developments. and that many fossils 
heretofore assigned to one, may be ultimately found to 
belong to the other. Ihave decided, therefore, to desig- 
nate these strata provisionally by the name of the lo- 
cality where their fauna are most richly represented. 
It must not, however, be inferred that the strata so des- 
ignated are the only ones found at Rochdale, for at least 
the Trenton, and the Hudson river groups are also well 
represented there. The rocks of the ‘*‘ Rochdale” group 
are apparently found everywhere in this limestone belt. 
5. The Trenton limestone, found quite fossiliferous 
at Wallace’s quarry, Salt Point, at Pleasant Valley, 
Rochdale and at Newburgh, and generally in the Wap- 
pinger limestone. 
6. The Utica slate may be present in the county, 
though the fossils found along the banks of the Hudson 
river, and assigned to this group are thought by some 
experienced paleontologists to belong quite probably to 
the Hudson river group, on the ground of having been 
actually found in several places mingled with organic 
remains characteristic of the latter horizon. 
7. The Hudson river shales prevalent in every part of 
Dutchess county. 
97 
