SUBMARINE DEPOSITS 197 



formed of such terrigenous and neritic deposits as are now 

 being laid down within 200 or 300 miles of land, on the 

 continental shelf and the upper part of the continental slope, 

 and do not include to any marked extent deposits which 

 closely resemble those now accumulating in the abysses of 

 the Atlantic and the Pacific oceans. 



This conclusion has an important bearing on the contro- 

 versial subject known as the permanence of the continental 

 ridges and the ocean basins. As most of the sedimentary 

 rocks of past geological times were of marine origin, there 

 is no doubt that the greater part of the continental land 

 of the globe has been at one time or other, or even at various 

 times, at the bottom of the sea, and no doubt considerable 

 areas that were once land are now submerged. Land and 

 sea have been occasionally changing places throughout the 

 ages. But that fact does not necessarily imply that contin- 

 ental land ever occupied the great ocean basins, or that 

 deep-seas once rolled over what are now continents. The 

 study of the ocean depths and of the deposits from abyssal 

 regions does not (in Sir John Murray's opinion, with which 

 most oceanographers would agree) give any support to the 

 view that vast continents have disappeared in what are now 

 oceanic areas. 



The contrary view — that continents and ocean basins 

 have changed places in the past, and have even followed one 

 another like successive waves round the globe — has been held 

 from time to time. The myth of a " lost Atlantis " dates 

 back at least to the time of Plato, and has been revived 

 many times since ; while a sunken continent, " Gondwana- 

 land," has been supposed to occupy the Indian and Southern 

 oceans in order to account for the distribution of geological 

 formations and living organisms. 



The stories of sunken lands and the legends of spectral 

 or floating islands in the west are probably based partly 

 on the evidence of submergence seen on the western coasts 

 of Europe. The old river-beds of the Shannon and other 



