234 The Physical History of the Trias 



The extent of these several areas, moreover, and the coarse- 

 ness of the conglomerate composing them, seem connected 

 with the size of the valleys which traverse the crystalline rocks 

 westward of each deposit. Thus, on the Delaware, the largest 

 of the streams flowing down from these highlands, there is 

 exposed for two miles along the bank of the river an immense 

 deposit of this conglomerate, the stones composing it being in 

 some instances a hundred pounds in weight. 



From the above considerations, we conclude that these beds 

 are shore deposits, derived chiefly from the accumulation of 

 pebbles and rounded masses of rock, at the mouths of the rivers 

 which drained the highlands of New Jersey in Triassic times. 



These ancient rivers, like their modern representatives, must 

 have been impetuous mountain streams, capable of pushing 

 great quantities of rounded stones and other debris along their 

 beds. The transportation of material in this manner is exem- 

 plified at the present time by the carrying power of the Rock- 

 away river at Boonton. The slag from the iron works at this 

 place, situated just within the border of the crystalline rocks, 

 has for many years been thrown into the river, which has 

 washed it away, and carried thousands of tons of this material 

 for a distance of two or three miles down the stream. Where 

 the waters become broader and less impetuous, upon entering 

 the red sandstone country, the slag has been deposited in im- 

 mense quantities, so as greatly to obstruct the flow of the stream 

 and damage the adjacent meadows. 



A swift river, upon flowing into more quiet waters or meet- 

 ing the waves and currents of an estuary, would deposit the 

 stones and gravel brought down from the valley through which 

 it had flowed. Such an accumulation would have a fan-shaped 

 form, with its greatest thickness near the mouth of the river, 

 and becoming thinner and composed of finer material on its 

 outer margin. Should the current of such a river vary with the 

 seasons, or be affected by floods and drouths, the coarse mate- 

 rial would be carried farther from shore when the river-current 

 was swiftest. During seasons when the river was less energetic, 

 the deposit of mud and sand, brought in by the waves and 



