1872.] 



' Shearwater 3 Scientific Researches, 



563 



difference exists between the bottom-temperature of the North Pacific and 

 that of the North Atlantic, it is evident that if there ever was a time at 

 which a continuous Continent extended from Greenland to Scandinavia, the 

 North Atlantic would then have been cut off from the Polar basin almost 

 as completely as the North Pacific is now, and its bottom-temperature would 

 be higher than we now find it. If, on the other hand, there should ever 

 be such a subsidence of the Peninsulas of Alaska and Eastern Siberia, as 

 would open a free communication between the Arctic basin and the North 

 Pacific, the temperature of the lower stratum of the latter would probably 

 be greatly reduced. 



42. How important would be the Geological and Biological effect of such 

 changes, and how great a light may be thrown on Palaeontology by such 

 inquiries as I have indicated, was admirably shown by Mr. Prestwich in 

 the Presidential Address which he last year (1871) delivered to the Geolo- 

 gical Society. After pointing out how entirely the Thermal condition of the 

 Mediterranean differs from that of the Atlantic, in consequence of its 

 exclusion from the general Oceanic circulation, he suggests whether the 

 deep Sea in which the Chalk of Europe, with its more Tropical genera, was 

 deposited may not also have been a sea shut out from direct communication 

 with Arctic seas. As the Cretaceous Ocean formed an east and west belt 

 across the present Continents of Europe and Asia, we must look for " dry 

 " land on the confines of that ocean ; and it is probable that the latter may 

 " have been, to the north, in the direction between Greenland and Scotland 

 " and Scandinavia, where the present ocean is some hundreds of fathoms 

 •* shallower than further south. We know that towards the end of the 

 " Cretaceous period a change took place in the Fauna, arising apparently 

 " from the shallowing of the sea that preceded the deposition of the Maes- 

 " tricht beds. Many of the great Cephalopods disappeared, and Reptiles 

 M increased in numbers ; at the same time the Lamellibranchiate Mol- 

 " lusca became more predominant. " . ..." If such a northern land 

 " barrier as that which I have alluded to existed at the period of the Chalk, 

 " and that barrier was submerged during the early part of the Tertiary 

 " period, it would (taken in connexion with the very different conditions 

 " of depth under which the Chalk and Lower Tertiaries were formed) go far 

 " to account for the great break in the Fauna of the two periods. Some years 

 " since I had occasion to show on other grounds that the Thanet Sands, 

 " which repose on the Chalk in the South-east of England, exhibited a 

 " Fauna essentially of temperate or cold latitudes ; and I inferred the inset 

 " of currents from the north." 



43. It is regarded by Mr. Prestwich as highly probable that the old 

 Cretaceous ocean was prolonged into the American Cretaceous area, across 

 the present Atlantic ; and he thinks " that the hypothesis with regard to 

 " the continuity of that sea-bed from the period of the Chalk to the present 

 " period is one of high probability." Now this continuity is all that it was 

 intended by Prof. Wyville Thomson and myself to express by the phrase 



