FKTTKE, MANHATTAN SCHIST OF NEW YORK 247 



rests unconformably upon the pre-Cambrian gneisses. This is followed 

 conformably by a limestone known as the Wappinger, which in turn is 

 succeeded by a thick series of shales belonging to the Hudson River group.. 



POUGHQUAG QUARTZITE 



The Poughquag quartzite reaches a maximum thickness of about six 

 hundred feet. It is usually a compact, granular silicified quartz sand- 

 stone of medium grain, with occasionally a fine conglomerate at the base 

 and sometimes finer grained quartzitic shales at the top. Its fossil con- 

 tents show that it is of Lower Cambrian age.'^^ 



In certain places, as along the Matteawan inliers of pre-Cambrian gneiss', 

 a coarse granitic stratum rests on the upturned gneiss, and this is fol- 

 lowed by a somewhat foliated, finer grained quartzitic rock. This granitic 

 stratum has been interpreted by C. E. Gordon^^ as representing decayed 

 portions of the old pre-Cambrian gneisses which were pa,rtly reworked 

 by the advancing Cambrian sea and later covered by quartzitic sands. 



IJsuall)'', wherever the relationship of the quartzite to the gneiss can be 

 made out, the contact is seen to be an unconformity, and it is evident that 

 the foliated stiTicture of the gneisses dates back to a period of folding 

 prior to the deposition of these Lower Cambrian sediments. 



Since the deposition of the quartzite, the region has been involved 

 in extensive thrust faulting which has shoved the older pre-Cambrian 

 gneisses upon the later formations. In some cases, the quartzite moved 

 with the gneiss, while in others the gneiss moved over it. The quartzite, 

 although never violently folded, was nevertheless greatly disturbed by 

 orogenic movements in certain places. 



WAPPINGER LIMESTONE 



Following the Poughquag quartzite just north of the Highlands comes 

 the Wappinger limestone. In this region, it has a thickness of about one 

 thousand feet. Portions of it are magnesian in character. A belt of this 

 limestone runs from the Hudson Eiver in a northeasterly direction along 

 the northwestern margin of the Highlands and then turns northerly up 

 the Clove Valley where it dies out. To the east of the Clove Valley, it 

 passes underneath a thick series of phyllites and schists, appearing again 

 farther east in the Dover-Pawling Valley. 



C. E. Gordon^"^ has identified fossils of Lower Cambrian, Beekmantown 



^ J. D. Daxa : Am. Jour. Sci., 3rd ser., Vol. 3, pp. 250-256. 1872. 



^ "Geology of the Poughkeepsie Quadrangle." N. Y. State Mas. Bull. 148, p. 46. 1911. 



^ IMd., p. 71. 



