THE BIOTITECRANITES. 171 



ones. Oil the otlu-r luuid, Wowlder.s of the former are often fouml in the 

 lower beds of the latter. 



Since the granites and their accompanying gneisses can not be the 

 foundation upon the surface of which the materials of the green schists were 

 spread, and since these latter are all fragm'eiital volcanic rocks and surface 

 lavas, it follows necessarily that there must have been a basement beneath 

 the green schists wliich is i^lder than these and the gneissoid granite that 

 intrudes them. This basement, however, has not )et been identified in 

 the Northern Complex. Occasionally a small mica-schist ledge is met with 

 in the midst of granite ledges, and this may represent a series of rocks 

 underh'ing the green schist and older than they; but no evidence either in 

 favor of this view or in opjjosition to it has yet been collected. 



THK BlOTITBGllANITES. 

 PETRUGRAPHICAL CIIAIiACTKR. 



Macroscopicai. — As lias alrcadv bceu stated, the more massive and the more 

 schistose phases of the granites — the gneissoid granites and tlie granitoid 

 gneisses — are believed to be portions of the same rock mass, and therefore 

 they are discussed together. Further investigation may show that some of 

 the gneisses are older than some of the granites, Init up to this time no 

 discrimination between the massive and the schistose granites has been 

 attempted in mapping. 



The rocks vary in color from grayish-green to bright-red, the color of 

 the former varieties being due to tlie abundance of chlorite in them. Their 

 feldspar is rarelv white. It is usually of a light-red or pink color. "When 

 brio-ht-red it fives the entire rock of wdiicli it is a part a red tint, which 

 varies in briUiancy according to the quantity of feldspar in it. In a few 

 instances bright-red orthoclases are scattered through a groundmass of gray 

 granite, but this variety is usually found only near the contacts of the rock 

 with the greenstones or in its apophyses that intrude the latter. 



Microscopical. — The grauites and their gneissoid varieties are ali composed 

 of clouded orthoclase, microcline, plagioclase (the first-named mineral 

 predominating), quartz, and brownish-green biotite or its decomposition 



