124 Belemnitella Americana and Mucronata [322 



and the conclusion arrived at that chalk is a deep-sea oceanic forma- 

 tion exactly analogous to that which has been shown to cover large 

 areas of the Atlantic, Pacific, and Southern oceans. 



" But there are several objections to this view which seem fatal to 

 its acceptance. In the first place, no specimens of Globigerina-ooze 

 from the deep ocean-bed yet examined agree even approximately with 

 chalk in chemical composition, only containing from 44 per cent, to 

 79 per cent, of carbonate of lime, with from 5 per cent, to 11 per cent, 

 of silica, and from 8 per cent, to 33 per cent, of alumina and oxide 

 of iron. Chalk on the other hand contains usually from 94 per <;ent. 

 to 99 per cent, of carbonate of lime, and a very minute quantity of 

 alumina and silica. . . . Sir Charles Lyell well remarks that the 

 pure calcareous mud produced by the decomposition of the shelly 

 coverings of mollusca and zoophytes would be much lighter than 

 argillaceous or arenaceous mud, and being thus transported to 

 greater distances, would be completely separated from all impurities 

 . . . Mr. J. Murray . . . says . . . ' The Globigerina-oozes which we 

 get in shallow water resemble the chalk much more than those in 

 deeper water.' Mr. GUvyn- Jeffries, one of our greatest authorities on 

 shells, taking the whole series of genera which are found in the chalk 

 formations, seventy-one in number, declares that they are all com- 

 paratively shallow-water forms, many living at depths not exceeding 

 40-50 fathoms, while some are confined to still shallower waters." 



Wallace discusses the occurrences of the chalk in the two 

 great areas, from Antrim to Crimea, and from Sweden to 

 Bordeaux, and says it is absurd to suppose that these areas 

 were oceanic abysses, since we have good evidence for believ- 

 ing there was land in Germany and in several of the nearby 

 regions. Moreover, the frequent intercalations of sandstones 

 and conglomerates, limestones, marls, and muds, contain- 

 ing many of the same fossils as the chalk do not add to the 

 abyssal theory. Finally, he says, the wide-spread emergence 

 at the end of the Mesozoic, evidenced by unconformities which 

 point to a Europe very similar in outline to that of today, 

 would make it extremely unlikely that there had been any 

 depths over Europe comparable to the present-day oceanic 

 abysses. Wallace of course makes no mention of the modern 

 theories of isostatic equilibrium which support his theory 

 admirably by the doctrine of the permanency of oceanic basins. 

 He reaches the conclusion that the chalk was a deposit laid 



