1883.] 469 [Crosby. 



ancient representative of the modern calcareous or Globigerina 

 ooze found in all the great oceans at depths varying from 250 

 to nearly 3,000 fathoms. The chief objection which he raises is 

 that the chalk and ooze differ widely in composition ; and analy- 

 ses are quoted to show that the ooze is, on the average, poorer in 

 calcium carbonate, and richer in silica, alumina, and iron than the 

 chalk. In these chalk analyses, however, no account has been 

 taken of the flints, which may be fairly regarded as representing 

 the silica in the ooze, the flints being due to the segregation of 

 finely divided silica which was originally uniformly diffused 

 through the chalk. The silica, therefore, may be at once stricken 

 from the list of differences between the chalk and ooze. 



The Cretaceous age closed several millions of years ago, a time 

 long enough to permit considerable changes in the character of 

 the deep sea oozes. The alumina and iron in the Globigerina 

 ooze are chiefly the insoluble residue of the volcanic dust spread 

 every where over the ocean-floor ; they form a part of all marine 

 formations, and the fact that they are conspicuous constituents 

 of the calcareous ooze simply implies that the Foraminifera shells 

 accumulate with extreme slowness at the present time. To make 

 the ooze chemically identical with the chalk, we have only to 

 increase the rate of the organic deposition. But Mr. Wallace has 

 already done this for the Cretaceous period ; for he shows, first, 

 that the abundance of the pelagic Foraminifera, of the calcareous 

 tests of which both the chalk and the ooze are mainly composed, 

 is, other things being equal, proportional to the temperature of 

 the water ; and, secondly, that the Cretaceous seas of Europe 

 were very warm. He conceives that a land barrier stretched 

 from Scandinavia to Greenland, concentrating the Gulf stream 

 and directing it across the site of modern Europe. 



Mr. Wallace's explanation of the chalk of Europe embraces 

 propositions that are not easily reconciled. For he insists, and 

 rightly, upon the great purity of the chalk, and yet holds that it 

 was deposited in a shallow and narrow sea, and consequently 

 near large bodies of land. He derives the chalk in large part 

 from the comminution of coral-rock, and yet names only two 

 points in Europe (Maestricht in Belgium and Faxoe in Denmark) 

 where coral-reefs of Cretaceous age may be observed, and refers 

 to no modern coral-reefs where chalk is now forming in this way. 



