DEEP-SEA DEPOSITS 81 



eruptions. Related factors are the much discussed 

 ''turbidity currents" referred to above. Moreover, in 

 certain locaHties there exist, even in great depths, bur- 

 rowing animals like mud-eaters which delve into the 

 uppermost sediment layers, where they may disturb, in 

 certain cases even efface, boundaries between the dif- 

 ferent strata. Finally, bottom currents of various origins 

 have a tendency to stir up sediment particles already 

 settled and prevent fresh particles from coming to rest, 

 especially where such bottom currents are intensified 

 by passing over a submarine mound or ridge. When one 

 is reading the records of the deep, the possible effects of 

 all these disturbing elements on the sequence and struc- 

 ture of the strata must be considered. 



Let us for a moment assume that the dismal fate 

 intimated in Chapter 1 has actually overtaken our earth, 

 namely that all the water masses of its oceans have dis- 

 appeared. A trip by caterpillar jeep over the ancient 

 sea bottom would be fairly rough going. Hills and hum- 

 mocks would jut up through the sediment, and we 

 might find ourselves negotiating steep slopes. In certain 

 regions, as in the central Atlantic Ocean, mighty moun- 

 tain chains equaling in length the Andes and Rockies 

 together would rise before us. If we were to knock off 

 fragments from these submarine mountains, we would 

 find them composed of a material different from that of 

 the continents. Mafic and ultramafic rocks from deep 

 layers of the earth's crust would predominate. 



However, the most interesting material to be met with 



