58 Ailing — Problems of Adirondack Precambrian. 



shown on Bear Pond Mountain in the Paradox Lake 

 quadrangle is an excellent example of this ancient erup- 

 tive. 



The Laurentian Granite 



The existence of a granite much older than the Algo- 

 man series of eruptives seems to the writer to have been 

 sufficiently proven to need but little comment. Its uni- 

 versal habit is to be intricately involved with the Gren- 

 ville series. This ledthe early geologists to regard it as 

 a Grenville sediment. 19 Even today this view is held 

 by Miller, 20 but the recognition of pegmatitic phases of 

 the rock threw the first doubt upon its sedimentary char- 

 acter . . . while the chemical analysis settled the ques- 

 tion." 21 



The Laurentian granite apparently has its best devel- 

 opment in the northwestern Adirondacks in contrast to 

 the southern and eastern areas. There is evidence that 

 there are two distinct periods of metamorphism. One 

 followed the intrusion of the Laurentian granite and the 

 other the intrusion of the anorthosite-syenite-granite- 

 gabbro series. The intensity of the metamorphism of 

 the earlier period apparently was more severe in the 

 northwest than in the southwest. In contrast to this the 

 disturbance that came later was more pronounced in the 

 southeast. Thus in the north and northwest the Lauren- 

 tian rocks are folded and foliated together with the 

 Grenville while the later igneous rocks are much less 

 metamorphosed. This makes the distinction between the 

 two groups possible in the northwest while it is a difficult 

 matter to distinguish the two granites in the south- 

 eastern area, for both series suffered metamorphism 

 together. This in part accounts for the different views 

 held by Cushing and Miller. 



That an old granite does occur in the southeastern 

 Adirondacks the writer feels positive; Cushing's work 

 in the Saratoga sheet was found by the writer to have 

 been exceedingly well done; the Laurentian granite is 

 there. The presence of the old granite was very common 

 on most of the graphite properties. The rock that 

 directly underlies the Hague gneiss (garnet-sillimanite- 



19 Cushing, H. P. : N. Y. State Mus., Bull. 77, pp. 17-19, 1905. 



20 Miller, W. J.: N. Y. State Mus., Bull. 182, p. 11, 1916. 



21 Cushing, H. P. : N. Y. State Mus., Bull. 169, p. 21, 1914. 



