NEW ENGLAND APPALACHIAN SYSTEMS 



L50 



the western portion of Poughkeepsie quadrangle, but farther east, cleavage 

 seems to have destroyed them. Hudson River slates of black, gray, greenish, 

 and red color are known; commonly, argillaceous layers are interbedded with 

 thousands of thin, fine-grained sandy layers, or aphanitic cherty beds that 

 weather whitish. Scattered through the series are hundreds of lenses of sand- 

 stone, or quartzite, conglomerate, and graywacke, and quartz veins penetrate 

 the rock in almost every outcrop. On account of the intricate folding, and 

 absence of continuous exposures, the thickness of the Hudson River series is 

 unknown, but it may exceed that of the carbonate rocks below. 



Balk's interpretation of the structure of the region may best be under- 

 stood by the study of the lower cross section of Fig. 11.9. Of first im- 

 portance is the unconformity at the base of the Poughquag quartzite 

 which clearly reveals the Precambrian age of the gneiss and granite com- 

 plex of the Hudson and Housatonic highlands. 



The highlands are regarded as uplifted blocks. As the uplift occurred, 

 the Paleozoic succession along the west side was tilted westward, and in 

 addition was broken by a number of faults, most of which are thrusts of 

 medium to steep southeasterly dip. Thrust faults are also recognized along 

 the east flank of the northeast end of the Hudson highland. That the 

 Precambrian highlands are uplifted masses is shown by the general basin 

 distribution of the youngest rocks, the Hudson River pelites, in the middle 

 of the intervening areas, and then the next older rocks, the Wappinger 

 limestone and Poughquag quartzite next to the gneiss. 



Between the Hudson and Housatonic highlands is a Paleozoic area 

 which is regarded as a faulted syncline. It has the special significance of 

 affording a connection between the known Cambrian and Ordovician 

 strata on the west of the highlands to unfossiliferous and more meta- 

 morphosed strata on the east, and it is here that Balk and Barth have 

 demonstrated the progressive metamorphism of the Hudson River slates 

 and phyllites to schist and even injection gneisses, and the increase in 

 marmorization of the carbonates. 



The general basin structure of the strata between the masses of Pre- 

 cambrian gneisses is greatly marred and distorted by normal and thrust 

 faults which have cut the quartzite for miles along the gneiss borders, 

 and at many places have brought the limestone to the level of the pelite. 

 Most of the faults strike north-northeast or north-south; hence, the rock 





CAMBRIAN 5ERIES 



CANADIAN SERIES 



CHAZYAN SERIES 



LOWEST MOHAWKIAN (PAMELIA) LIME- 

 STONE ON PRE- MOHAWKIAN GEOLOGY 



Fig. 11.6. Cambrian and Ordovician paleogeography of the New York and St. Lawrence 

 region, after Kay, 1942. The ruled areas represent the spread of deposits, and the Taconic 

 allochthone as postulated in Figs. 11.12 and 11.13 is shown in both present ^left) and 

 original (right) position. 



