Ailing — Problems of Adirondack Precambrian. 57 



in origin. The writer examined some specimens taken 

 just south of Canton. His conclusion is in accord with 

 Martin. There are some geologists who entertain the 

 view that some of the red granite of St. Lawrence County 

 is Laurentian in age. If this is true it would suggest 

 that in the orthoamphibolite inclusions we are dealing 

 with a very old eruptive. In the Long Lake quadrangle 

 Cushing found gabbros whose borders were amphibolitic 

 while the cores were hyperitic in character. In discuss- 

 ing their probable age relations he says that he " never 

 found these amphibolitic gabbros in connection with the 

 great intrusives [Algoman], never except in association 

 with the granitic gneisses [Laurentian], the Grenville 

 rocks possibly excepted. The difference [between the 

 two types of gabbros] may perhaps be accounted for on 

 the supposition that the inclosing granitic gneisses were 

 less effective as a protecting buttress against the stresses 

 producing metamorphisni, than were the massive and 

 bulky anorthosites and syenites. And while this may be 

 true and the two gabbros, notwithstanding their differ- 

 ences, be of the same age, it seems a much less likely 

 supposition than that the one gabbro is much older than 

 the other and its more profound metamorphism thus to 

 be accounted for." 17 



This was written before the recognition of the granite 

 gneiss as Laurentian but it is just as clear a statement as 

 one recently made to the writer. " There is certainly 

 much [ortho-] amphibolite in the region which is older 

 than the Laurentian and is the oldest eruptive present, 

 so far as I know." 18 



Of course Cushing' s observations pertain in large 

 measure to the northern and northwestern Adirondacks. 

 In the eastern and southeastern areas the presence of 

 the old metagabbro has not been emphasized. The 

 writer encountered metagabbros on the graphite proper- 

 ties. Some metagabbros, especially in the southern dis- 

 tricts, "Whitehall and Saratoga sheets, were proven by 

 field relations to be of post-Laurentian granite, pre- 

 Algoman age. These are discussed later on. Others, 

 however, apparently more metamorphosed, although not 

 definitely assigned to the older metagabbro, may very 

 well be so classified. The orthoamphibolite extensively 



17 Cushing, H. P. : N. Y. State Mus., Bull. 115, p. 466, 1907. 

 "Cushing, H. P.: personal correspondence, November, 1917. 



