3() NEW YORK STATE MUSEUM 



A tabic of analN'ses of Adirondack diabases has been recently 

 ])ublished by Kemp, to which reference may l)e made by snch as 

 are interested in this snbject.^ 



STRUCTURES OF THE PRECAMBRIC ROCKS 



Foliation. The foliation or cleavage, the most conspicnous 

 structure of the Precambric rocks, is found in sediments and 

 igneous rocks alike, the trap dikes excepted. But the sediments 

 are better foliated than the igneous rocks. The foliation of the 

 Grenville rocks of the Saratoga region is parallel to the bedding, 

 so that the directions of the two are equivalent. This seems to be 

 the general relation of the two in the Adirondacks, as suggested 

 years ago by Van Hise.- 



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°. The strike swerves to the northwest in the 

 northeast portion of the ([uadrangle, and to the northeast in the 

 northwest portion, though the dips remain to the south. This is 

 not in accord with the usual direction in the Adirondacks where 

 the prevailing strikes are northeast. As elsewhere a great mono- 

 cline of the rocks is suggested; and, as elsewhere, this makes a 

 Grenville succession of enormous thickness, so thick as to suggest 

 caution in interpretation of the structure and as to emphasize the 

 probability of the alternative suggestion that the rocks are closely 

 ])inched and folded, in a series of closed, overturned folds. 



Faults. The great faults of the district are of much later date 

 than the Precambric, and dislocate Precambric and Paleozoic rocks 

 alike. But here, as elsewhere in the region, small faults are noted 

 in the Precambric rocks of such character that they seem surely 

 of Precambric age. We have found as yet no certain evidence of 

 large faults of this early date. 



PAT.EOZOTC ROCKS OF THE WESTERN TROUGH 



BY IT. P. GUSHING 



The terms eastern and western troughs as used in this report 

 have no significance other than convenience in description, and 

 imply merely the relative positions of two contrasted sets of 



^ N. V. State Mus. lUil. J38, p. 60-61. 



- I'. S. Gcol. Siirv. i6tli Ann. Rep't, pt i, p. ^^j-^. 



