TRANSPORTATION OF DEBRIS. 



215 



deposited, as compared with the distances traveled by finer detritus. In- 

 stances where stones weighing from two to five pounds have traveled .50 

 miles are common. Where ice is the vehicle, the distance may be almost 

 indefinitely great. It would seem to require extraordinary circumstances 

 to justify the belief that a conglomerate could be formed as far as 50 miles 

 from the sources of its fragments, and it is probable that most of the strati- 

 fied beds are formed in the very neighborhood of those sources, though 

 beds of small gravel, graduating into coarse and then into fine sandstone, 

 may extend away much farther. 



Transportation. — Transportation by ice, whether floating, or moving 

 upon the land, forms a subject by itself, and has no analogy to the agency 

 of water in moving debris. It will therefore be passed over, since it takes 

 no part in the operations which are the object of this discussion. The 

 movements ot the coarse materials which build up conglomerates differ 

 from those of the finer sediments, though they have something in common. 

 The greater portion of the fine silt, much of the fine sand, and the whole 

 of the chemical and organic precipitates are carried by moving waters in 

 suspension, and are thrown down when the waters come to rest. The 

 coarser materials are impelled along the bottoms of rivers and the shelving 

 floors of the ocean and lakes near the beaches. Here the want of habitual 

 observation and common experience is apt to mislead us and render diffi- 

 cult the obtaining a just apprehension of the nature and magnitude of this 

 impulsion. An}^ day we may see the rivers turbid with earthy matter, and 

 it is an easy step from this observation to the great generalization that the 

 land is wasting away and heavy strata accumulating beneath the ocean. 

 But it is not so easy to see what goes on beneath the water. The times 

 when the processions of stones are on the move are times of high water, 

 and flooding rains, when geologists are as prone as other people to seek the 

 kindly welcome of roofs and closed doors; times when the deep and murky 

 waters prevent us from seeing and the roar of the torrent from hearing the 

 movement, even if we ventured out to watch it. Thus, the process is not 

 a matter oi common and direct experience; nay, experience might seem at 

 first to lead us to a contrary conclusion. When a stream is low and clear 



