26 NEW YORK STATE MUSEUM 



of plutonic rocks. They are batholiths or great, deep seated 

 volume, of irregular shape. The included fragmenis of older 

 rocks which have from time to time been detected demonstrate 

 their intrusive nature. These and the nature of the intrusive con- 

 tacts give such clues to their relative ages as can be obtained. The 

 original outlines of the intrusions, that is, the evidence as to whether 

 they ever assumed the laccolithic or other definite shapes, have 

 been rendered wellnigh undecipherable by faulting and erosion. 



Granites and related types 



There are several areas to wliich this name has been distinctively 

 applied. While they are described before the anorthosites and other 

 eruptives their relations to the latter are obscure. In general they 

 are believed to be older, but there is little ground, for this belief 

 other than their intimate association with the Grenville. Their dis- 

 tinction from the acidic members of the syenite series is, moreover, 

 not in all cases clear; and the possibilities of the occurrence of shales 

 and f eldspathic sandstones in the Grenville, vvliich might yield,, upon 

 extreme metamorphism granitic gneisses, have not been overlooked. 

 Nevertheless both in the field and in the laboratory the occurrences 

 here colored and described as granites, have impressed themselves 

 as sufficiently distinctive to justify the procedure. 



The largest area is in the southeastern corner of Bulwagga moun- 

 tain. A biotite granite is very abundant all through this portion of 

 the sheet, so much so as to be the predominant rock. While it may 

 not be the exclusive member, the variations can not well be shown 

 in colors. Excellent exposures appear near the iron bridge at the 

 headwaters of Grove brook. In their section microcline is the 

 most abundant mineral while quartz and biotite practically com- 

 plete the slide. This combination is in contrast with the mineralogy 

 of the other groups of eruptives. Both microcline an:! biotite are 

 seldom seen in the latter^ and the inference is natural that when 

 they predominate we are dealing with a separate intrusive. 



In the western portion of the area colored green, red granitic 

 rocks have been observed, which reveal under the microscope no 

 dark silicates, but which have only finely striated plagioclase and 

 quartz. A few decomposition products, perhaps from dark sili- 

 cates, and a few tiny zircons complete the slide. 



Throughout this granitic area much pegmatite is present and the 

 granites are often cut by it. 



About 3 miles north of Port Henry another area of small dimen- 



