GEOLOGY OF THE VICINITY OF LITTLE FALLS 19 



would indicate that originally they were sandstones, generally 

 more or less shaly. In many of them the quartz is now found in 

 thin, regular leaves separated by very finely granular feldspar, 

 and such '' leaf gneisses," -as Dr F. D. Adams of the Canadian 

 Survey has happily styled them, are a very conspicuous feature 

 of the Grenville rocks. However, the severe metamorphism to 

 which most of the pre-Cambrian rocks have been subjected has 

 recrystalized much of their quartz in the leaf form, both in those 

 of igneous as well as in those of sedimentary origin, so that this 

 character can not be regarded as in any sense indicative of origin. 

 It is naturally best exhibited b}^ rocks rich in quartz, and some 

 rocks which were likely granites originally show it in great per- 

 fection. 



The darker colored rocks would seem to have been shales and 

 calcareous shales originally. They must have contained a small 

 amount of carbonaceous matter, very possibly of organic origin, 

 now metamorphosed to graphite. Many ordinary shales and lime- 

 stones contain carbonaceous matter, so that the supposition is a 

 very natural one. 



These Grenville rocks are very like rocks which Kemp has 

 recently described from Warren and Washington counties, to the 

 eastward, where they also occur in abundance, and where 

 limestone is relatively scarce. From the standpoint of one who 

 is familiar with but one of the two districts and necessarily 

 depending on descriptions for a knowledge of the other, the rocks 

 would seem identical in the two areas, and not unlikely the whole 

 pre-Cambrian fringe on the south side of the Adirondacks will be 

 found to be characterized by abundant Grenville rocks with a 

 scarcity of limestone. 



Probable igneous rocks associated with the Grenville. At most 

 of the Grenville exposures of any extent, rocks which are 

 regarded as igneous are found mingled with them. They are 

 always thoroughly gneissoid and are interbanded with the old 

 sediments. They are thought to represent old dikes and sheets 

 of igneous rock, possibly surface flows also, which were formed 

 during, or not long after the deposition of the sedimentS; and 



