REPORT OF THE DIRECTOR I9I7 US 



gist terms a " gneiss." The interpretation of these gneisses fur- 

 nishes the professional worker one of the most difficult problems in 

 the whole region. 



The Gneisses 



Although limestone is reported near Colby pond (plate i), the 

 writer did not find any remnants of this interesting and ancient 

 formation " in place " in the immediate neighborhood of the pond, 

 but in the vicinity of the town of Saranac Lake patches of the gneisses 

 were found in the bed of the river. 1 Better exposures can be found 

 in the bed of the river three-eighths of a mile north of Bloomingdale, 

 where the gneiss contains flakes of graphite, and on the southwest 

 slopes of Mount Pisgah, where the schists, rich in mica, and the 

 quartzites are splendidly shown, (plate 2) Moreover, one may 

 easily pick out quartz boulders, which were part of the original 

 sandstone and various boulders of gneisses that in many- cases were 

 shales, conglomerates or the result of their intermediate sediments. 



We do not know what was the nature of the rock floor upon which 

 the Grenville rocks were laid down, nor are we acquainted with the 

 order of events that took place in that far distant past. The rocky 

 book that the geologist is trying to decipher is at the best fragmen- 

 tary and many leaves are absent. But enough remains of this old 

 series of sedimentary rocks to make us sure that it was of great extent 

 and of enormous thickness. One geologist estimates that it may 

 have been from 20,000 to 25,000 feet thick. 2 We find strata which 

 in all probability belong to this same Grenville series in New England, 

 in the Highlands of the Hudson (West Point region) , and in Canada, 

 and can safely assume that it exists at great depths throughout 

 New York State overlaid by rocks of later ages. 



The Doubt jul Gneisses 

 North of the town of Saranac Lake there are a variety of gneisses 

 and granitelike rocks that are today a puzzle to the most observant 

 and careful worker. Some of these may be igneous in nature (that 

 is, were once in a molten condition), while others are sedimentary 

 (that is, water-laid) in origin, but great changes have subsequently 

 taken place in all of them so that their appearance and composition 

 is far different from their original form. If a trace of the floor of 



1 Petrographic examination seems to cast some doubt upon this interpreta- 

 tion, although Doctor Cushing regards it as undoubted Grenville. 



2 H. P. Cushing, N. Y. State Mus. Bui. 95, p. 275. 



