550 DEEP-SEA DEPOSITS. 



course of riveT-s, hence theaccuraulations of ooze, sand, and gravel, well 

 known under the name of alluvium, which border difiterent portions of 

 tlieir course, and the even and level surface of which recall the cover- 

 ing of water which has s})read them out. 



At the mouth of the rivers, in the sea as in lakes, the retard in 

 velocity of the waters effects the operation in the most marked man- 

 ner; therefore plains of alluvium are specially developed in these 

 places. 



The alluvium is not restricted to this border; it is formed in the oi)en 

 sea by the action of a transportation effected by waves, tides, and 

 currents more or less constant. These motions affect also the deposits 

 which come from the ocean coasts. We learn this from the marine 

 maps which give, together with the ocean depths, the nature also of 

 its bottom as it has been determined by soundings. Exaiuination of 

 these maps shows that the deposits in question are spread out usually 

 in flat form and constitute the real submarine plains, com))arable with 

 the slimy and even plains existing at the mouth of rivers. Such are, 

 for example, the bottom of the English Channel and the deposits which 

 border France in the ocean. 



Thus the sea may be considered as an immense work-room of tritu- 

 ration, of transportation and deposition. It produces on a large scale 

 the same effect that takes place over a distance of a few kilometers in 

 the bed of a torrent. Deposition is finally effected in the relatively 

 calm regions of the ocean basin. 



In this incessant work of demolition the liquid waters have also very 

 active co-laborers whose importance is not recognized in temperate 

 countries such as we dwell in. They are the masses of ice which 

 accumulate in the valleys around the mountainous masses covered 

 with i)erpetual snow. In spite of their apparent immobility, these 

 glaciers, of so impcKsing and magnificent an aspect, have a descending 

 movement, slow and continuous. Thus they constitute, on account of 

 their solid state and their enormous weight, even more than li(juid 

 water, most energetic agents of wear and transportation. In tlic 

 region not far from the i)ole, the part performed by glacial torrents and 

 floating ice permeated with fine detritus throughout their mass is 

 specially recognizable 



The Norwegian ex])edition, the labors of which have been i)ublished 

 under the direction of the eminent professor, Mohn,* has very clearly 

 determined the facts in question, so far as concerns Si)itzbergen, Ice- 

 lan<l, and Greenland. The ooze from the glacial trituration extends 

 over the wliole bottom of the North Atlantic, and seems to form its 

 chief sediment as far as 30° of latitude. The presence of similar 

 deposits has been ascertained along the coast of North America, and 

 in the Southern Hemisphere as far as about 40°. 



* Den Norake Nordhouse Expedition, 1S76, 1878, 9th ed., p. 70. 



