4 Quaternary Formations of Southern New Jersey, 



Thus the Great Plains at the east base of the Rocky Mountains 

 are more or less generally covered with gravel for scores of 

 miles — in places more than ioo miles — from the mountains. 

 The surface about an isolated mountain is, in some cases, so 

 strewn with debris from the mountain, that nothing but this 

 debris is visible at the surface for miles about it. The plains 

 east of the Andes and south of the Himalayas afford good illus- 

 trations of subaerial deposition on a large scale, if the phe- 

 nomena of these regions have been interpreted correctly. 



Perhaps no region affords more striking illustrations of pluvial 

 and fluvial sedimentation than the Great Basin region of the 

 United States. The steepness of the slopes of the Basin Ranges 

 of mountains, the flatness of their surroundings, the relative 

 freedom of their slopes from vegetation, the great changes of 

 temperature which disrupt the rock, and the fitful nature of the 

 precipitation, all contribute to this end. The result is. that the 

 plains about and between the mountains are covered, many of 

 them deeply covered, by the debris washed out from the moun- 

 tains. At the immediate bases oi the mountains these accumu- 

 lations are said to be, in exceptional cases, more than a thousand 

 feet deep. Their depth decreases with increase of distance 

 from the mountains, but is very considerable even scores of miles 

 away in some cases. The Coastal Plain deposits under con- 

 sideration have many features in common with the deposits at 

 the bases of mountains, though they are on a much smaller 

 scale. 



The principles involved. — The essential principles involved in 

 the development of the Quaternary formations of the Coastal 

 Plain, according to the interpretation here favored, are perhaps 

 best understood hy a few simple illustrations. 



Let us suppose a plain, recently covered by a formation of 

 sand and gravel, to be brought into such a position as to be 

 subject to effective erosion. This might be brought about in 

 various ways, as by the relative uplift of the region which had 

 been the site of deposition. Let it be supposed that a vigorous 

 master stream runs along the lower side of the area, and that 

 tributaries to this stream descend across the plain, at right angles 



