Crosby.] 470 [November 7, 



The Oahu deposit belongs to the past and is very small, twenty 

 to thirty feet across and eight to ten feet thick and entirely des- 

 titute of Foraminifera. The chalk contains no corals, nor frag- 

 ments of corals, nor does it shade off at the borders into coarser 

 calcareous rocks composed of broken coral; and in no modern 

 ocean are the coral-reefs entirely converted, as fast as formed, to 

 an impalpable slime or ooze. If all this occurred, as Mr. Wallace 

 imagines, in the Cretaceous Mediterranean of Europe, the force 

 of the waves and currents must have been sufficient to transport 

 the finer debris of the land long distances from shore, but this 

 supposition is negatived by the great purity of the chalk. 



Sir Wyville Thomson, from whose reports on the voyage of 

 the " Challenger " Mr. Wallace quotes, and to whom the calcare- 

 ous ooze analyses were known, evidently failed to discover the 

 great disparity between the ooze and the chalk, for he says : U 'I 

 imagine, however, that the limestone which would be the result 

 of the elevation and slight metamorphosis of a mass of Globiger- 

 ina ooze would resemble very closely a bed of gray chalk ; " per- 

 haps as closely as it is reasonable to expect, considering the 

 enormous lapse of time between the two deposits. 



The truly abyssal deposit of the modern ocean is the red clay 

 which is found at nearly all depths below 2,500 fathoms and, ac- 

 cording to Sir Wyville Thomson, covers not less than ten million 

 square miles of the ocean-floor. In the " Challenger " report Sir 

 Wyville expresses the opinion that*a deposit of this red clay might 

 come to be very like one of the Paleozoic schists. But, appar- 

 ently, he did not hold this view long ; for at the meeting of the 

 British Association for the Advancement of Science, in August, 

 1878, he concluded an account of the deep sea clay as follows: 



" So far as we can judge, after a most careful comparative examination, 

 the deposit which is at present being formed at extreme depths in the ocean 

 does not correspond either in structure or in chemical composition, with any 

 known geological formation; and, moreover, we are inclined to believe, 

 from a consideration of their structure and of their imbedded organic re- 

 mains, that none of the older formations were laid down at nearly so great 

 depths — that, in fact, none of these have anything of an abyssal character. 

 These late researches tend to show that during past geological changes 

 abysssal beds have never been exposed, and it seems highly probable that 



1 Voyage of the " Challenger," vol. n, p. 256. 



