m EXPEDITION OF THE "CHALLENGER" 103 



whole effect of the discoveries made since his time 

 has been to compile a larger and larger comment- 

 ary upon this text. It is, at present, a perfectly 

 tenable hypothesis that all silicious and calcareous 

 rocks are either directly, or indirectly, derived from 

 material which has, at one time or other, formed 

 part of the organized framework of living organ- 

 isms. Whether the same generalization may be 

 extended to aluminous rocks, depends upon the 

 conclusion to be drawn from the facts respecting 

 the red clay areas brought to light by the 

 Challenger. If we accept the view taken by 

 Wyville Thomson and his colleagues that the 

 red clay is the residuum left after the calcareous 

 matter of the Globigeriruz ooze has been dissolved j 

 away then clay is as much a product of life as / 

 limestone, and all known derivatives of clay may ( 

 have formed part of animal bodies. 



So long as the Globiyerince, actually collected at 

 the surface, have not been demonstrated to con- 

 tain the elements of clay, the Challenger hypo- 

 thesis, as I may term it, must be accepted with 

 reserve and provisionally, but, at present, I cannot 

 but think that it is more probable than any other 

 suggestion which has been made. 



Accepting it provisionally, we arrive at the 

 remarkable result that all the chief known con- 

 stituents of the crust of the earth may have 

 formed part of living bodies ; that they may be 

 the " ash " of protoplasm ; that the " rupes saxei " 



