90 NEW YORK STATE MUSEUM 



is more uniform in character than the Grenville series, lacking the 

 limestones, quartzites and certain gneisses which appear largely 

 in that series and being mainly composed of acid, orthoclase- 

 gneisses. 1 



In commencing work in the Adirondack region, this classifi- 

 cation was taken for a working hypothesis. As work has pro- 

 gressed, the gneisses which it was thought might represent Logan's; 

 fundamental gneiss have been partially separated into their con- 

 stituent elements, and in every case the separated element has 

 been found to be of igneous origin, and to be intrusive into, and 

 therefore younger than, the Grenville rocks. This has recently 

 been strongly emphasized by Smyth, as a result of his work along 

 the better exposed belts of the Grenville rocks on the west.* 

 There still remains, however, a great body of gneiss of uncertain 

 relationships, evidence respecting its age not being forthcoming- 

 as yet. Nor has its origin been demonstrated, though apparently 

 no sedimentary rocks are represented in it, the gneisses through- 

 out having the mineralogy and composition of igneous rocks. It 

 may then be said that no rocks have been found in the northern 

 Adirondacks which can be shown to be older than the Grenville 

 series, but that in every case in which the relations have been- 

 made out, the adjacent rocks show intrusive contacts with the 

 Grenville rocks. On the other hand, that is a sedimentary series 

 and must have been laid down on some floor. 



The latest conclusions of the Canadian geologists respecting the 

 similar rocks in their territory are of great interest in this con- 

 nection. In a recent report on the geology of the area to the 

 north of Montreal, Prof. F. D. Adams says: 3 



Whether all these gneisses really form a portion of the floor 

 on which the Grenville series was deposited, since brought up by 

 folding and erosion, and thus entitled to the appellation " funda- 

 mental gneiss ", or whether they are intrusive masses, folded by 

 the pressure to which the whole region has been subjected, can 

 not be determined. 



lGeology of Canada. 1863. p. 839. 



215th an. rep't N. Y. state geologist. 1895. 1:481-97. 



SGeol. sur. Canada, new series, v. 8, pt J. p. 8-29. 



