THE BUILDING OF AN ISLAND. lOI 



with corals and other remains of sea creatures, are slowly accumulated, while 

 occasional deposits are brought down b}' streams from the remainder of the 

 land not yet under the water and are mingled with the shell sand or are laid 

 down as small beds of hard sand and gravel. Whether the whole of the land 

 ultimately went down under the water there is no means of ascertaining; 

 neither is it possible to say to what depth it sank. Down to the present time 

 no oceanic deposits, as in the case of Barbadoes, have been discovered in St. 

 Croix, and indeed it seems likely, from the frequent occurrence of pebbles 

 from the older rocks in the marl formation, that the latter was put down 

 during a period of slow subsidence. It does not seem likely, therefore, that 

 an oceanic deposit, if it existed here at all, would be found, as in Barbadoes, 

 between the limestones and the older rocks. However that may be, the sub- 

 sidence must have been a long one to allow of the deposition of the 600 feet 

 of limestones and marls which we now see, to say nothing of that large part of 

 the original deposit which must have since been swept away. 



After the long interval of subsidence comes another period of lifting 

 when the remnants of the second land, bearing on its surface the great accu- 

 mulation of limestones, is once more forced above the waves, this time, how- 

 ever, with much less disturbance of its strata than in the older uplifting move- 

 ment, and without intrusions of molten rock, or at all events with none that 

 were powerful enough to penetrate the limestones. Just as we asked in regard 

 to the sinking of the land, how deep it went under the ocean, so we may now 

 ask about the lifting, how high the land was raised. In an earlier chapter it 

 was mentioned that naturalists had concluded from the plants and land-shells 

 of the West Indian islands that they had at one time formed continuous land, 

 in which case the lift we are considering was probably very great. Dr. W. J. 

 Spencer, the American geologist already quoted, has arrived at the same con- 

 clusion on geological grounds. He says that the soundings off the coasts of 

 the Atlantic States show that the courses of the rivers flowing from the 

 mountains over the present coast plain, can be traced over the sea bottom far 

 out into the ocean to depths of thousands of feet, from which he concludes 

 that the land ofT the coast is a sunken plain, and he sees reason to believe that 

 the sinkinsf has extended through the Bahamas and the Caribbean Islands to 

 the South American coast. He believes that there is evidence to show that 

 there was a large plateau joining the two continents and having its highest line 

 towards the east while its drainage ran west into the Caribbean Sea. Hence 

 he regards the channels between the islands as former valleys, and the islands 

 themselves as remnants of a mountain chain which had been intersected by 

 the streams. He writes of " The West Indian bridge between North and 

 South America" and speaks of the present great depth of the channels as a 

 "yardstick" to measure the former heights of the mountains, which he 

 estimates to have been 10,000 to 12,000 feet or perhaps in some cases even 

 14,000 feet. These great elevations he believes were reached in Pliocene 

 times, after a previous sinking of the land subsequent to the deposition of the 



