52 NEW YORK STATE MUSEUM 



The chemical analyses also throw some light on the question of 

 their igneous or sedimentary nature. It will be observed that all 

 the rocks are rich in soda, even the most basic. Were they re- 

 crystallized sediments, they must have been derived from shales, 

 or in the most acidic cases, shaly sandstones, since no other sedi- 

 ments will give anything approximating these compositions. Yet 

 in the process of disintegration of feldspathic rocks and deposition 

 of the debris as sediments, the alkalies diminish greatly and of the 

 two, potash is customarily the survivor. Sediments of a com- 

 position such as these analyses afford, would be extraordinary, 

 whereas eruptive rocks not infrequently furnish parallels. 



Granite. This rock as an acidic extreme of the syenite series 

 has already been referred to. The field relationships of the speci- 

 men analyzed are best explained by this assumption. In the south- 

 eastern corner of the Elizabethtown quadrangle, there is, however, 

 as already set forth a quite extended area in which granitic rocks 

 are prominent. It has been mapped as a separate mass, although 

 the evidence of its individual intrusive character is not clear. The 

 subject is fully discussed under the topic of granites and related 

 types. They have a widespread reddish color and yield percentages 

 in quartz such as are possessed by the granites. 



In one of the two localities which have been studied with the 

 microscope the rock consisted of quartz and microperthite in great 

 preponderance. There were a few shreds of biotite and hornblende, 

 and rarely a grain of magnetite and a zircon. The rock was greatly 

 crushed and strained. This is the specimen which furnished the 

 analysis given as no. i under the syenites above. 



A second, a reddish rock from the southeastern corner of the 

 Elizabethtown sheet in the area mapped as granite, contained 

 greatly predominating quartz and finely twinned plagioclase. It 

 has already been mentioned under granites on a preceding page. 

 Orthoclase could not be identified. A few decomposition products, 

 believed to have once 'been bisillicates, and a few tiny zircons made 

 up the slide. The minerals showed abundant evidence of strains 

 and crushing. 



Basic gabbros 



This type of rock constitutes a large number of intrusions well 

 distributed along the border of the anorthosites and the other rocks 

 and sometimes in the anorthosites themselves. They are wide- 

 spread throughout the eastern Adirondacks and, although far less 

 large in amount than the anorthosites and syenites, are yet a char- 

 acteristic feature of the local geology. They appear chiefly as 



