CH. Ill] OOZE OF SHALLOW WATER. 159 



in ooze from a depth of many fathoms in mid-Atlantic it 

 is only 43 — 79 °/ . Chalk has a very small quantity of 

 silica, alumina and insoluble debris, while in ooze there 

 is 10 — 43 °/o of these substances. 



IV. Dr John Murray found that the ooze from shallow 

 water resembles chalk much more nearly than that from 

 depths over 1000 fathoms. Prof. Agassiz has described a 

 shore deposit largely derived from the dibris of coral rocks 

 which bears a very close resemblance to chalk ; and it is 

 possible that the chalk of Europe was to some extent at 

 any rate formed from the denudation of the coral reefs 

 which were so abundant during the oolite period. The 

 most striking instance which appears so far to support the 

 contrary proposition is the Radiolarian earth of the 

 Barbadoes, and perhaps of some of the other West 

 Indian islands. This overlies unquestioned sandstones 

 of tertiary origin; hence it follows that, since the be- 

 ginning of the tertiary epoch, the land immediately 

 surrounding those islands and the islands themselves 

 must have been depressed to a depth of at least 1000 

 fathoms. 



Evidence against the view that existing Oceans 

 have not largely changed their areas. 



There is another series of facts which have a bearing 

 upon the problems at issue, and which indicate, though 

 obscurely perhaps, a possibility that far back in time 

 there may have been a relative disposition radically 

 different from that now prevailing. 



