208 New York State Museum 



parallel belts. There are other important areas in the 

 east, in Essex county, and a number of scattered areas 

 on the north and south sides and in the interior. The 

 sedimentary gneisses have a distribution that corresponds 

 in general to that of the limestones on the border of the 

 Adirondacks where they are most widely distributed. 

 They also occur in certain areas in Warren and Wash- 

 ington counties where the limestone is found only occa- 

 sionally. The amphibolites or hornblende schists are in 

 part at least derived from shales, though some probably 

 originated from metamorphism of diabases or gabbros. 

 They are of less extent than the limestones and gneisses. 

 The quartzites occur on both the eastern and western 

 borders of the Adirondacks. In the east they are found 

 in Essex and Warren counties; in the west they occur 

 mainly in St Lawrence county, including the Thousand 

 Islands area. 



The igneous rocks of the Adirondacks are all later 

 than the Grenville sedimentaries and, while there is 

 doubt as to the relationships of the rocks in certain 

 areas, in general their order has been established as 

 gneisses, anorthosites, syenites, granites, gabbros and 

 diabase dikes {see introductory chapter on rocks). The 

 gneisses and gneissic granites are the oldest rocks in 

 the Adirondacks and no doubt underlie the Grenville 

 series as well as cut into them. Those in the north- 

 western section have been correlated with the Laur- 

 entian granites ; and here also belong extensive areas 

 of gneiss, especially in the northern Adirondacks. The 

 anorthosites have an extensive development in the 

 Adirondacks and with the exception of a few outlying 

 areas are included in the present area of Essex and 

 Franklin counties and cover about 1200 square miles. 



