White and Cope—The Green River Group. — 411 
most of the indurated rock of the St. Peter’s and Potsdam sand- 
stones; but in some cases there are indications that the indura- 
tion has followed lines of faulting, where the silica may be 
extraneous.* In the case of the Archean quartzites of the 
Baraboo region an extraneous source is suggested by the fre- 
quent occurrence in these quartzites of strings and veins of 
white quartz, often supplied with cavities lined with quartz 
crystals. 
University of Wisconsin, Madison, Wisconsin, February, 1883. 
Art, XLI—On the existence of a deposit in Northeastern Mon- 
tana and Northwestern Dakota that is possibly equivalent with 
the Green River Group; by CHARLES A. WHITE. 
[Published in advance by permission of the Director of the U. 8. Geological 
Survey. ] 
THE great fresh-water’ Eocene series of strata known as the 
Green River Group occupies, as is well known, a very large 
Utah and Colorado; but in the absence of positive evidence it 
may well be doubted whether the strata of that group ever ex- 
* See T. ©. Chamberlin’s description of the formation at Ironton, Wis., Geol. 
of Wis., vol. iv. ; 
* 
