FOLIATION IN THE PRE-CAM BRIAN OF NEW YORK 591 



According to Cushing, "the foliation strike over much of the 

 Saratoga quadrangle is nearly east-west, and the dips are to the 

 south and rather flat, seldom reaching 45 . As elsewhere, a great 

 monocline of the rocks is suggested, and, as elsewhere, this makes 

 a Grenville succession of enormous thickness, so thick as to suggest 

 caution in the interpretation of the structure, and as to emphasize 

 the probability of the alternative suggestion that the rocks are 

 closely pinched and folded in a series of closed, overturned folds." 1 

 It is, however, by no means necessary to assume that such common 

 occurrences of monoclinal dips may be due to isoclinal folding. 

 The breaking up and tilting of many blocks or belts of Grenville 

 strata into general parallelism with the upwelling bodies of magma 

 could quite conceivably have taken place under only very moderate 

 lateral compression at most, and, in such cases, monoclinal dips 

 are just what would be expected. This matter will be more fully 

 discussed below. 



In the Little Falls, Remsen, Port Leyden, and Lake Pleasant 

 quadrangles, which are also mapped in detail, the Grenville is 

 only sparingly represented, but none of the field evidence points to 

 profound folding of the strata due to lateral compression. 



The recent (1913-14) survey of the Blue Mountain quadrangle 

 by the writer has thrown important light on the structure of the 

 Grenville series which is there extensively represented. The 

 great Panther-Snowy mountain mass (altitude 3,900 feet) of syenite 

 occupying the southern portion of the Blue Mountain and the 

 northern portion of the Indian Lake quadrangles is completely 

 bounded on the west, north, and northeast by an unbroken belt 

 of Grenville (mostly limestone) whose strikes and dips show it to 

 lap up on the flanks of the mountain mass of igneous rock for many 

 miles. The curving strike of the igneous rock is also essentially 

 parallel to that of the Grenville. It is evident that we have here a 

 large-scale example of the raising or doming of Grenville over the 

 surface of the great body of uprising magma, the general cover 

 having been removed by erosion, leaving only the circumferential 

 belt of Grenville strata. The higher portions of the syenite now 

 rise fully 2,000 feet above the Grenville. This large-scale tilting 



1 H. P. Cushing, ibid., No. 169, 1914, p. 30. 



