3o8 C. N. FENNER 



on the eastern side of the river. The conglomerates here carry 

 quantities of shale mixed with the gravel. The old streams, of which 

 these are the beds, evidently deposited at times quantities of mud. 

 As the waters ceased flowing the mud was dried and baked till it 

 became well hardened. When the next rush of waters came some 

 of the strata of hardened mud withstood the force of the stream, but 

 others were broken up and the pieces mixed with the pebbles and 

 swept along with the current. From the recurrence of the phenomena 

 this must have happened time and again. 



The pebbles of the beds are mostly quartz, sometimes only 

 slightly rounded. Limestone is also of frequent occurrence.^ Often 

 weathered surfaces of the conglomerate show rounded cavities from 

 which limestone pebbles have been dissolved, and the general porosity 

 of the beds may be partly due to the solution of smaller lime grains. 

 The presence of these limestone pebbles indicates a not distant source, 

 but nothing from which they could have been derived is to be found 

 for many miles. The original strata were either totally broken up 

 and carried away or, more probably, were buried beneath later 

 deposits. 



It is to be noted that the pebbles are all of moderate size, rarely 

 more than six inches in diameter. No bowlder masses, like those 

 which are common in river channels, ancient and modern, in regions 

 of rugged relief, are to be found here. The trough of depression, in 

 which deposition Was proceeding, had been filled so that the surface 

 of the buried valley was now almost a level plain, on which the rush of 

 waters, even from torrential streams, soon lost its force. 



From the evidence of the rocks themselves at the base of the First 

 Watchung Trap we are able to picture, with a fair amount of certainty, 

 the character of the region and the conditions of the deposition of 

 strata preceding the period of the lava flow. We see on the east and 

 the west chains of hills of moderate relief, composed of the old crystal- 

 line rocks, whose surfaces gradually disintegrated under the effects 

 of the weather, and the detritus from which was carried down the 

 slopes and spread over the intervening valley. The climate was arid, 



I In a couple of pebbles of decomposed limestone which I found in these conglom- 

 erates there were abundant fossils. Crinoid segments were very numerous, and bryo 

 zoans were abundant. There was also a fragment which may have been the pygidium 

 of a trilobite. 



