184 Proceedings of the Royal Physical Society. 



more continuous — a broad belt extending in the direction of 

 the Pacific coast-line from Mexico up to high northern 

 latitudes. In short, before the Cretaceous period closed, the 

 major portion of North America had been evolved. A 

 considerable tract of what is now the western margin of the 

 continent, however, was still under water, while from the 

 Gulf of Mexico (then much wider than now) a broad 

 Mediterranean Sea swept north and north-west through 

 Texas and the Eocky Mountain region to communicate with 

 the Arctic Ocean. All to the east of tliis inland sea was 

 then, as it is now, dry land. Thus, up to the close of the 

 Cretaceous period, in America and Europe alike, oceanic 

 currents coming from the south had ready access across the 

 primeval continental plateau to the higher latitudes. Southern 

 Europe, indeed, during Mesozoic times, was simply a great 

 archipelago, having free communication on the one hand 

 across the low grounds of Central and ]^orthern Eussia with 

 the Arctic Seas, and, on the other, across vast regions in 

 Asia with the Indian Ocean. 



Of the other great land-masses of the globe our knowledge 

 is too limited to allow us to trace their geographical evolution 

 with any confidence. But, from the very wide distribution 

 of Mesozoic strata in South America, Africa, Asia, and 

 Australia, there can be no doubt that, at the time of their 

 accumulation, enormous tracts in those regions were then 

 under water. The land-masses, in short, were not so con- 

 tinuous and compact as they are at present. And although 

 we must infer that considerable areas of Mesozoic land are 

 now submerged, yet these cannot but bear a very small 

 proportion to the wide regions which have been raised above 

 the sea-level since Mesozoic times. In short, from what we 

 do know of the geological structure of the continents in 

 question, we can hardly doubt that they have passed through 

 o-eographical revolutions of a like kind with tliose of Europe 

 and North America. Everywhere over the great continental 

 plateau elevation appears, in the long run, to have been in 

 excess of depression, so that, in spite of many subsidences, 

 the tendency of the land throughout the world has been to 

 extend its mari]jins, and to become more and more con- 



