2() NKW YORK STATE MUSEUM 



I)rogressive increase in amount of nietamorphisni from west to 

 east, so tliat, when the eastern border is reached, the relations of 

 the rock groups to one another have become much disguised and 

 difficult to decipher. If this white rock be really an igneous 

 granite, then its relations to the (Irenville are apparently just those 

 which are diagnostic of the Laurentian in western New York and 

 in Ontario. The apparently confused commingling of the two 

 rocks, the apparent interbedding, and the abundant development of 

 pink garnet both in the schists and in the intrusive, are the expres- 

 sion of the greater severity of metamorphism. 



The syenite. The surface rocks of much of the Adirondack 

 region are intrusive igneous rocks of early Precambric age, but 

 younger than the Grenville and the Laurentian. There are four 

 groups of these rocks — anorthosite, syenite, gabbro and granite — 

 named in order of age. The first two occur in much greater volume 

 than the last two. In distribution, the anorthosite differs, from the 

 syenite in occuring chiefly in a single great bathylitic mass wdiose 

 area at the present-day surface is about 1500 square miles in the 

 eastern and central Adirondacks. There are small outlying masses 

 to be sure, but neither abundant enough nor large enough materially 

 to (|ualify the general statement. Idie southern edge of this mass 

 is well north of the Saratoga ([uadrangle so that, except for an 

 occasional glacial boulder, the rock is not found here. 



The syenite contrasts quite shar])ly with the anorthosite in dis- 

 tribution. Instead of appearing in one huge mass it forms many 

 small ones ; instead of being an ainmdant rock in part of the 

 region and wholl\' lacking in the remainder, it is found everywhere 

 throughout the Adirondacks. h>very detailed map of jxirt of the 

 region shows it present ; and we know also that it is abundantly 

 I^resent in the remainder wliich has Ijeen co\ered merely by recon- 

 naissance work. Because of this scattered distribution we are 

 wholly unable as yet to give any estimate of any value concerning 

 the area which the rock occu])ics ; we can, however, now say that 

 syenite is the surface rock of a much greater area in the Adiron- 

 (kicks than that occu])ied bv anorthosite, larije as the latter is, and 

 that tlie area of syenite is a notal)le one when compared with any 

 other known area the world over. 



There are three main areas of syenite within the mapped limits. 

 The largest is the one which forms the main mass of the Mt 

 McGregor range and its back country. Tlie modern gorge of the 



