QUARRY MATERIALS OF NEW YORK 57 



of a part of the Pottsville conglomerate in Pennsylvania. There 

 are no coal beds anywhere exposed and the conditions requisite 

 for their production did not become very general until after the 

 last of the local beds were laid down. The Carbonic strata are 

 limited to a small area in the extreme- southwestern section. The 

 long lapse of time that ensued to the close of the Carbonic and all 

 of the following Permic era find no record in the strata of New 

 York State. 



The Appalachian revolution brought Paleozoic time to an end 

 and marked the final emergence of practically the whole mainland 

 area of -New York from the sea. The disturbance resulted in a 

 broad uplift in the central and western parts of the State, but no 

 change in the relative attitude of the formations. In the southeast, 

 however, along the main axis it developed in some folding as shown 

 by the Shawangunk mountains. 



Mesozoic time was marked by only slight additions to the geo- 

 logical structure of the State. The Newark shales of late Triassic 

 age, which occur in Rockland and Richmond counties were prob- 

 ably formed in estuaries along the coast. During and after their 

 deposition, igneous activity was manifested by the intrusion of 

 diabase which, in places, reached the surface. The Palisades con- 

 sist of the exposed edge of a diabase sill intruded along shale and 

 sandstone beds of Newark age. With the last, or Cretacic, period 

 of Cenozoic time came the deposition of the older clays of Staten 

 Island and Long Island. 



During the Cenozoic interval there were small accumulations of 

 Tertiary clays in the same areas. The most important event of the 

 era in its influence upon the local geology, occurred in the Quatenary 

 period with the change of climate that brought on an ice invasion. 

 This advanced from north to south and spread over the whole 

 State, overriding even the higher mountains. The ice eroded away 

 the loose materials accumulated by weathering and also transported 

 immense quantities of rock which it plucked from the bared sur- 

 faces. The contours were rounded off and the land covered with 

 a mantle of clay and boulders (till), the transported materials 

 being also heaped up in the form of hills and ridges which are 

 known as moraines and drumlins. The drainage was also obstructed 

 or remodeled ; some large lakes occupied the main river valleys for 

 a time, as in the Hudson valley. The main effect of the ice upon 

 the rock surface was to remove the evidences of the long pre- 

 ceding period of weathering ; consequently the rock outcrops appear 

 much fresher than they do in the unglaciated territory to the south 

 of New York. 



