THE NEWARK ROCKS 49 



The constitution of the arkose sandstones near Trenton and 

 beneath the Palisades shows that the sediment was derived 

 chiefly from older crystallines on the southeast, but scattered 

 limestone and sandstones pebbles derived from the southwest 

 show that the currents had a northward trend along the south- 

 eastern border. Along the northwestern border, where it is not 

 marked by faults, the material was evidently derived from the 

 adjacent rocks on the northwest. 



The constitution of the Newark beds points to the conclu- 

 sion that in pre-Newark times the old land surface was deeply 

 covered with residuary material, the product of long-continued 

 subaerial decomposition. On the crystalline areas it was chiefly 

 quartz and feldspar or kaolin. The limestone was buried beneath 

 a mantle of clay. In both cases the residuary products had been 

 formed chiefly by chemical agencies. The sandstone and quartz- 

 ite rocks were less affected by chemical changes and relatively 

 more by mechanical agencies. Their surface was, therefore, 

 covered by subangular fragments, due chiefly to the rending 

 action of frost and expansion and contraction with changes of 

 temperature. The almost complete absence of gneissic pebbles 

 with the presence of quartz, feldspar and partially disintegrated 

 ferro-magnesian minerals in the conglomerates, sandstone or 

 shales proves that the crystalline rocks must have been deeply 

 covered with a mantle of residuary material, so that streams, 

 although they had velocity enough to carry pebbles two or three 

 inches in diameter, did not corrade the bed rock, but worked in 

 the residuary material. 



The bulk of the Newark beds is so great as to indicate that 

 these residuary products must have been very thick. Their 

 accumulation was aided by gentle slopes, hindered by steep 

 declivities. Previous to the formation of the Newark beds the 

 neighboring land surface seems to have been one of low relief, 

 with gentle slopes, across which transportation was reduced to a 

 minimum. In other words, the land surface was approaching 

 the peneplain stage. 1 Had the land been high and the slopes 



1 Practically the same conclusion has been reached by Professor Davis in regard 





