GEOLOGY OF HAMILTON, WARREN AND WASHINGTON COUNTIES 159 



deserve much more detailed study than we have been able to 

 give them, and, when this has been done, the genetic and struc- 

 tural problems can no doubt be pushed well along toward solu- 

 tion. The gneisses embrace some varieties that are certainly 

 altered sediments. The latter are thinly schistose, richly mica- 

 ceous and often abundantly provided with quartz. They exhibit 

 in many exposures marked evidence of severe dynamic metamor- 

 phism, and have evidently been subjected to extremely powerful 

 compression. When broken parallel with the schistosity, they 

 show the small surfaces along which individual lenses have 

 slipped and rubbed. Results like these are characteristic of de- 

 formation in the zone of fracture and under comparatively small 

 load — according to the phraseology and conceptions established 

 by Van Hise. 



Other varieties of gneisses are more massive and seem to have 

 suffered less granulation. They present varieties consisting of 

 quartz, hornblende orthoclase and plagioclase and are less cer- 

 tainly derived from sediments. In a number of exposures appears 

 the coarse variety with the large lenses of quartz in the midst 

 of microperthite, which has been met in the northern Adiron- 

 dacks, particularly by Prof. Cushing near Franklin Falls, Frank- 

 lin co. This variety of rock is probably an altered conglomerate. 



In the vicinity of the crystalline limestones, quartzites or 

 quartzose gneisses appear which are beyond question metamor- 

 phosed sandstones, and which will be referred to under series 2. 



We have also met a few exposures of the dark green gneisses, 

 which are regarded as metamorphosed augite syenites, such as 

 ivere referred to in our last report as the " Whitehall type." The 

 exposures, so far as observations go, are not specially numerous, 

 but additional fieldwork may disclose more of them. 



The western line of the town is not easily reached without 

 camping, a mode of operation which we have been unable to 

 adopt, but there is little doubt from our observations in Hamilton 

 county, as shown by the maps elsewhere printed in this report, 

 that the gneisses cover practically all this portion. There may 

 l^e however, specially on the northeast, developments of anortho- 



