50 NEW YORK STATE MUSEUM 



so formed chiefly quartzite and limestone conglomerates. But 

 the rivers drained large areas of deeply disintegrated crystalline 

 rocks, and furnished from this source the bulk of the deposit over 

 the sea floor. No evidence of glacial action can be found in con- 

 nection with the massive conglomerate beds, which are undoubt- 

 edly the work of the waves and shore currents. They do not 

 belong to any single horizon but are shoreward correlatives of 

 the various shales of the middle of the estuary. 



The deposition of the sedimentary beds was interrupted by at 

 least three great lava flows, separated by long intervals of quiet 

 during which sedimentation continued as before. These lava 

 flows did not reach the New York area, but were restricted to New 

 Jersey. At some period, probably after the surface flows, great 

 sills of molten rock were intruded into the shales, and, if the 

 Ladentown trap be the continuation of the Palisades sill, the 

 greatest of them probably reached the surface in a small area at 

 its northwestern extension. 



The period of sedimentation was brought to a close by the 

 elevation of the beds above sea level. This was accompanied by 

 tilting and gentle folding but not by volcanic phenomena. The 

 faulting is believed to have occurred at the same time. The 

 nature of the elevating force is not well understood. The view 

 which connects the tilting and faulting with widespread move- 

 ments in the underlying rocks, by virtue of which the old surface 

 was so deformed that the Newark sediments settled down on it 

 as they could, seems best to accord with all the facts. 

 . Since their elevation they have been greatly eroded. The con- 

 structional surface consequent on the faulting and folding has 

 entirely disappeared. The region has been base-leveled once, 

 elevated, parts of it base-leveled again and again elevated. Leav- 

 ing out of account the comparatively slight modifications due 

 chiefly to the glacial period, the present topography is the result 

 of sub-aerial denudation. Thousands of feet of strata have been 

 worn off from the present surface. The hills and ridges owe their 

 hight solely to the fact that their rocks have better resisted the 

 agent of denudation than have the rocks in the valleys. 



