FRESH-WATER STREAMS. 653 



but the final shaping of the heights has been due to erosion, and 

 mostly, as has been stated, to erosion by fresh waters. This cause 

 has been in action ever since continents began to be ; and it has been 

 thus making earth and gravel for stratified rocks, as well as gorging 

 hills and mountains. The Appalachians have lost by denudation much 

 more material than they now contain. Mention has been made of 

 faults of ten thousand feet or more, along the course of the chain, from 

 Canada to Alabama. In such a fault, one side was left standing ten 

 thousand feet above the other, enough to make alone a lofty mount- 

 ain ; and yet now the whole is so levelled off that there is no evidence 

 of the fault in the surface-features of the country. The whole Appa- 

 lachian region consists of ridges of strata isolated by long distances 

 from others with which they were once continuous. Fig. 103, p. 96, 

 and Fig. 1134, p. 786, represent cases of this kind. The anthracite coal- 

 fields of central Pennsylvania were once apart of the great bituminous 

 coal-field of western Pennsylvania and Virginia (Fig. 613, p. 310). 

 They now form isolated patches ; and formations of great extent have 

 been removed from over the intervening country. The Wahsatch, 

 Uintah, and other related mountains of the Rocky Mountain region 

 have been spoken of as remnants of great formations that once covered 

 the country to a much higher level ; and probably the portion left is 

 not a hundredth part as great as that which has been carried off by 

 the plundering waters. And all this erosion was accomplished after 

 the commencement of the Tertiary era. 



In New England, there is evidence of erosion on a scale of vast 

 magnitude, since the crystallization of its rocks. On the summit-level 

 between the head-waters of the Merrimac and Connecticut, there are 

 several pot-holes in hard granite ; one, as described by Professor Hub- 

 bard, is ten feet deep and eight feet in diameter, and another twelve 

 feet deep. They indicate the flow of a torrent for a long time, where 

 now it is impossible ; and the period may not be earlier than the 

 Quaternary. Many other similar cases are described by Hitchcock. 



These examples of denudation are sufficient for illustration. The 

 other continents furnish cases that are no less remarkable. 



2. Transportation; Deposition. 

 1. Material transported and deposited. 

 The matprials transported by running waters are (1) stones, pebbles, 

 sand, and clay or earth ; (2) logs and leaves from the forests, and 

 sometimes trees that have been torn up or dislodged by the current ; 

 (3) mollusks or their shells, worms, insects, etc., attached to the logs 

 or leaves ; (4) occasionally larger animals, that have been surprised 

 and drowned by freshets, or bones that have been exhumed by the 

 waters. 



