GEOLOGY OF FRANKLIN COUNTY 115 



In the northern part of the county, that part mapped as occu- 

 pied by the doubtful gneisses, there is a good deal of granite. No 

 very large masses have been noted, but there are several small 

 ones which send out tongues into the adjacent gneisses, and from 

 these a series of gradations into exposures showing the gneiss 

 all cut up by small stringers of granite which run in general 

 parallel to the foliation; the phenomena being in short precisely 

 such as are common all over the world where these very old rocks 

 are exposed. 



1 mile west of Duane postoffice and a few rods south of the road 

 is a low cliff facing south, showing a rather fine grained, red 

 granite cutting amphibolite gneiss (see pi. 7). The granite cuts 

 vertically across the strike of the gneiss for the full hight of the 

 cliff (12 feet), incloses fragments of it and sends offshoots into it. 

 Like most of the granite of the county, it is essentially a quartz 

 feldspar rock, the amounts of magnetite, biotite and hornblende 

 being very insignificant. The feldspar is mainly microperthite, 

 but there is considerable microcline and a little oligoclase. The 

 rock is much metamorphosed. 



The gneiss is essentially a plagioclase-hornblende-augite rock. 

 Extinction angles up to 20° indicate an acid labradorite as the 

 feldspar. The augite is not so abundant as the hornblende, but 

 in considerable amount, of green color with slight pleochroism. 

 The rock is not to be distinguished from -the gneissoid phases of 

 the hyperite gabbros except for the absence of garnet, usually (not 

 always) abundant in the other rock. The age of the granite is 

 correspondingly uncertain, though of course it is younger than the 

 gneiss which it cuts. Just across the creek, 200 rods to the south- 

 west, the same rock association appears. 



For a wide area around St Regis Falls and Dickinson Center 

 the prevailing rock is an amphibolite gneiss identical with that 

 just described. Sometimes all pyroxene is lacking, sometimes 

 hypersthene is present in place of augite. These gneisses are all 

 cut up by granite which appears in small bosses or else in thin 

 bands in the excessively contorted gneisses. The granite varies- 

 much in grain, being at times quite coarse, as at St Regis Falls 



