6 Transportation of Sediments. 



production of much fine floury sediment. Ice-filled 

 valleys are thus deepened and widened, and much sedi- 

 ment is formed, and brought within reach of the trans- 

 porting power of rivers. Great blocks of stone and finer 

 debris that fall from the hills on the surfaces of glaciers, 

 are carried steadily onward in long lines till they reach 

 the ends of these ice-rivers, where they form terminal 

 moraines, and often, as fast as the mounds accumulate, 

 these are proportionally wasted by the streams that flow 

 from the ends of the glaciers. 



In cold climates, where special glaciers descend to 

 the sea, bergs break off often laden with blocks and 

 finer sediments, and floating seaward they deposit their 

 freights where they chance to melt. The breaking up 

 of the ice-foot on sea-coasts, and of river ice, also trans- 

 ports large quantities of matter and scatters it abroad. 



The quantity of material degraded and spread in 

 the sea by these united means is immense, and consists 

 of mud, sand, gravel, and rounded, subangular, and 

 angular blocks, often polished, grooved, and scratched ; 

 and from the irregular mode of its accumulation, and 

 the frequent grounding and scraping of icebergs along 

 the sea-bottom, the whole of this matter, if exposed, 

 would present one of the rudest forms of stratification. 



But the chief agent in the transportation of sedi- 

 ments from higher to lower levels is running water. 

 Great thunderstorms, water-spouts, and sudden thaws 

 in snow-covered lands, frequently produce startling 

 effects, stripping large areas bare of soil, and hurrying 

 to lower levels vast masses of earth, shingle, and 

 boulders. 



Every one who has looked at large rivers knows that 

 they are rarely pure and clear. The cause of this is 

 obvious. All rain, especially if long continued, exercises 



