32 W. B. D wight — Recent Explorations, etc. 



1. The Archaean of Stissiug and Fishkill Mountains, and of 

 other elevations. 



2. The Olenellus group (Georgia group of Vermont), 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 I have called the Calcifer- 

 ous, because I consider it manifestly most closely related to 

 what has been generally covered by that title. It is evident 

 however that the proper limits of both of the terms " Calcifer- 

 ous " and " Chazy " (as also of the entirely vague title " Quebec 

 group,") are undergoing severe review in the light of recent de- 

 velopments, and that many fossils heretofore assigned to one, 

 may be ultimately found to belong to the other. I have there- 

 fore decided to designate these strata provisionally by the name 

 of the locality where their fauna are most richly represented. 

 It must not, however, be inferred that these are the only strata 

 found at Rochdale, for at least the Trenton and the Hudson 

 Eiver strata are also well represented there. The rocks of the 

 Rochdale group are apparent^ found everywhere in this lime- 

 stone belt. 



6. The Trenton limestone, found richly fossiliferous at Wal- 

 lace's quarry, Salt Point, at Pleasant Valley, Rochdale, and 

 New burgh, and generally, in the Wappinger limestone. 



7. The Utica slate may also 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 paleon- 

 tologists to belong quite probably to the Hudson River group 

 on the ground of having been actually found in several places 

 mingled with organisms characteristic of the latter group. 

 There are also strong stratigraphic reasons for doubt as to its ' 

 presence here. 



8. The Hudson River shales, prevalent almost everywhere 

 in Dutchess county. 



This review of the latest paleontological facts, makes it evi- 

 dent that the strata in Dutchess County are simply the continu- 

 ation of the strata characterizing the Taconic and adjoining 

 series lying northward. But while proving a grand unity, they 

 indicate also an interesting and unexpected variety of rock- 

 structure. 



