CH. Ill] OCEANIC ISLANDS AND SUBMERGED CONTINENTS. 157 



II. It seems to be well ascertained that no oceanic 

 islands are formed of stratified rocks belonging to early 

 geological periods. They are in the main either of recent 

 volcanic or coral formation. Sir Archibald Geikie in 

 reviewing the Abbe - Renard's petrological work upon the 

 rocks of the island of St Paul in the Atlantic in Nature 

 some years back entitled his review, " A search for a lost 

 continent with a microscope." But no amount of research 

 either with or without a microscope has ever revealed the 

 slightest traces of a pre-existing continent in the oceanic 

 islands of any of the great oceans. On the other hand it 

 has been found that certain islands, once regarded as 

 purely oceanic, are in reality not so. This is the case 

 for example with New Caledonia, which contains both 

 palaeozoic and mesozoic rocks, though it is isolated by 

 water exceeding 1000 fathoms in depth. But these few 

 instances do not invalidate the general conclusion. Yet 

 two possible criticisms must be borne in mind; in the 

 first place we are not as yet in possession of all the 

 requisite knowledge about all the islands in question ; in 

 the second place we can imagine a subsidence of a large 

 continental tract which would leave above the surface of 

 the water no trace of its continental origin. If Africa, as 

 Mr Blanford points out, were to be submerged 2000 

 fathoms below the sea only a few elevations would remain ; 

 these are Mt Kilimanjaro, the Camaroons, and a few 

 other peaks; these mountains it must be remembered 

 are purely volcanic in structure and would give no 

 clue to the fate which had overtaken the surrounding 

 land. 



