EXPEDITION OF THE CHALLENGER. 43 



and iron namely, clay for the "chalk" that would otherv.'isc be 

 formed. 



If the Challenger hypothesis, that the red clay is the residue left 

 by dissolved Foraminiferous skeletons, is coi'rect, then all these de- 

 posits alike would be directly, or indirectly, the product of livnig 

 organisms. But just as a silicious deposit may be metamorphosed into 

 opal or quartzite, and chalk into marble, so known metaraorphic agen- 

 cies may metamorphose clay into schist, clay-slate, slate, gneiss, or 

 even granite. And thus, by the agency of the lowest and simplest of 

 organisms, our imaginary globe might be covered with strata, of all 

 the chief kinds of rock of which the known crust of the earth is com- 

 posed, of indefinite thickness and extent. 



The bearing of the conclusions which are now either established, 

 or highly probable, respecting the origin of silicious, calcareous, and 

 clayey rocks, and their metamorphic derivatives, upon the archaeology 

 of the earth, the elucidation of which is the ultimate object of the 

 geologist, is of no small importance. 



A hundred years ago the singular insight of Linnaeus enabled him 

 to say that "fossils are not the children but the parents of rocks,"* 

 and the whole effect of the discoveries made since his time has been 

 to compile a larger and larger commentary upon this text. It is, at 

 present, a perfectly tenable hj^pothesis 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 organisms. 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 Mr. Wyville Thomson and his col- 

 leagues that the red clay is the residuum left after the calcareous 

 matter of the Glohigerince ooze has been dissolved 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 Glohigerince, actually collected at the surface, have 

 not been demonstrated to contain the elements of clay, the Challenger 

 hypothesis, as I may term it, must be accepted with reserve and pro- 

 visionally, 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 constituents of the crust of the earth may have 



' " Petrificata montium calcariorum non filii sed parentes sunt, cum omnis calx oriatur 

 ab animalibus." " Systema Natura?," Ed. xii., t. iii., p. 154. It must be recollected that 

 Linnaeus included silex, as well as limestone, under the name of "calx," and that he 

 would probably have arranged diatoms among animals, as part of " chaos." Ehrenberg 

 quotes another even more pithy passage, which I have not been able to find in any 

 edition of the " Systema" accessible to me: "Sic lapides ab animalibus, nee vice versa. 

 Sic rnpes saxei non primsevi, sed temporis filias." 



