PERMANENCE OF CONTINENTS 89 



that part of the submarine pkun which is still under water, 

 this lowland of the southern Atlantic coast-lands is extremely 

 level with a slight dip toward the ocean depths, and a faintly 

 undulating surface, the irregularities not usually causing a 

 difference of altitude in one square mile of more than five or 

 six feet. Examining into the materials which compose this 

 emerged portion of the continental shelf, we find that they 

 consist in large part of detritus which the waves and rivers 

 have worn away from this land, and conveyed a little w^ay 

 from the ancient shore, together Avith quantities of fossils 

 which in their lifetime dreAV their solid parts from the sea- 

 water. Although nowhere else do we find any other so 

 perfect and extensive a fragment of the continental shelf 

 lying above the level of the sea, there is here and there 

 about the ereat lands evidence that this is the common nature 

 of these deposits. We may therefore conclude that they are 

 mainly made up of sediments brought to the sea from the 

 neighboring hills and plains of the land. 



Until within recent times geologists have generally held to 

 the opinion that the lands and seas had occasionally changed 

 positions, so that the continental areas were from time to 

 time lowered into the deep, and the floors of the abysmal 

 ' seas, by a similar alternating movement, lifted into the realm 

 of the air. The researches of Dr. Murray and others appear 

 to indicate that this alternation of relations does not occur. 

 Nowhere on the land have we yet found clear evidence going 

 to show the existence of any deposits such as are formed in 

 the abysmal regions of the ocean. The students of the 

 subject are now coming to believe that, while the continents 

 have been subjected to frequent oscillations, portions of the 

 surface of each becoming depressed to a moderate depth 



