4:66 T. G. Brown — Shawangunk Conglomerate. 



More recently Grabau has assigned these beds to a continental 

 or non-marine origin and placed a hiatus or disconformity 

 between the upper member and the overlying cement beds and 

 limestones.* 



All of the authors referred to above have studied these beds 

 either in natural outcrops or in exposures uncovered in the 

 Rosendale-Whiteport Cement region. One feature, which 

 throughout this whole region conceals the true relations of 

 adjacent beds, seems to have been undervalued in these descrip- 

 tions and that is the faulting of the region. Almost innumer- 

 able faults cut up and complicate the geolog} 7 of this region. 

 Both gravity and thrust faults are present, but the thrust faults 

 predominate. These range all the way from a few feet up to 

 several hundred feet in throw. Moreover, the effect of fault- 

 ing is not confined to fault planes or fault fractures superin- 

 duced upon the rocks at the time of faulting, but movement 

 has frequently taken place along the bedding planes. These 

 fault movements seem to favor the bedding planes between the 

 beds of different physical character and they often obscure the 

 natural transition between successive beds. Perhaps faulting 

 near the contact has given the impression that the change from 

 Shawangunk conglomerate to High Falls shale is more abrupt 

 than it really is. The same is true of the transition above to 

 the Binnewater sandstone and from this to the overlying 

 cement beds or limestones. 



Description of sections. — The studies on which this paper 

 is based were commenced in the summer of 1906, under the 

 direction of the Department of Geology of Columbia Univer- 

 sity. They were continued through two full years from 1907 

 to 1909, while the writer was employed by the New York City 

 Board of Water Supply as inspector of test borings during the 

 preliminary survey and as a member of the engineering field 

 force during the construction of the Rondout Siphon shafts 

 and tunnels. A large number of core borings were drilled and 

 five shafts were sunk in whole or in part through these beds. 

 These offered exceptionally good opportunities for observing 

 the relation of these beds in their natural unweathered and 

 undisturbed condition and of making accurate measurements 

 of the thickness at different points along a line some two 

 and one-half miles in length. 



The present paper will consider only the formations included 

 between the unconformity at the top of the Hudson River shale 

 and the base of the Upper Silurian limestones or cement beds. 

 In this region these formations include three distinct members. 

 At the base comes the Shawangunk conglomerate with a 



* Jour, of Geol., vol. xvii, No. 3, p. 252, 1909. 



