GEOLOGY OF THE VICINITY OF LITTLE FALLS 23 



textiore is usually of local development in deep seated igneous 

 rocks, that mucli of the rock at Little Falls lacks it and is 

 thoroughly gneissoid, hence presenting an intermediate stage be- 

 tween the rock at Middleville and that of the main mass, and that 

 in the great syenite masses of the central Adirondacks the bulk of 

 the rock is not porphyritic, and the porphyritic development is 

 local; also these are, at least in part, demonstrably of considerably 

 j^ounger age than the Grenville rocks. 



Moreo-ver, as has been stated, this syenite is almost equally hard 

 to distinguish from the greenish gneiss of syenitic composition 

 found so closely associated with the Grenville sedimentaries, and 

 the granitic and gabbroic gneisses that accompany them. While 

 thm greenish gneiss is regarded as an igneous rock, it seems quite 

 certain that its age association with the sedimentaries is close, as 

 is also that of the accompanying granitic and gabbroic gneiss. It 

 is also true of these latter that they are certainly much older than 

 the gabbros and some granites which occur in the mid- Adirondack 

 xegion, and it would seem therefore that the same might well be 

 true of the syenite also. The green gneiss is regarded as being of 

 tMs earlier age, so th-at there seem to be syenite rocks of at least 

 two different ages in the Adirondack pre-Cambrian. But the 

 -writer is in doubt with regard iK> the syenite mass of the northeast 

 part of the map, though disposed to regard it provisionally as 

 Ijelonging to the earlier period and to correlate it with the green 

 gneisses of the Grenville. In regard to the rock at Little Falls 

 and Middleville, he is also in doubt, th'ough here with a disposi- 

 tion to refer to the later period, and to correlate with the later 

 syenite of the central Adir«ondack region. The whole matter is 

 one of great difficulty, and no decisive evidence for either view 

 has yet been forthcoming anywhere. 



Pre-Cambrian antlier northeast of Little Falls. There is exposed 

 beie a gray gneiss with a slight greenish tinge. The exposure is 

 very small and shows but the one sort of rock. It is in the main. 

 a quartz feldspar rock, not more than 5fc of other minerals being 

 pr^ent, mostly magnetite, biotite, and a decomposed mineral 

 which was likely a pyroxene. Quartz makes some 20,^ of the rock. 



