Io6 TROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



came originally to Australia from an antarctic continent. It is 

 highl}' probable that many other forms of terrestrial life besides the 

 Mesozoic flora originated in the southern hemisphere; and unless a 

 very considerable area of what is now deep ocean was occupied by 

 land in Mesozoic and Palaeozoic times, a change in favour of which 

 there appears but slight evidence, it is far from improbable that 

 the Antarctic continent was the original area of development. 



The land-areas of the present day may differ in one important 

 particular from those which existed at earlier periods of the earth's 

 history. With the exception of America and Australia, all the great 

 laud-masses are joined together in the northern hemisphere, and 

 there cannot be a question that the division in the case of America 

 is of extremely recent date ; for, as I have already mentioned, a con- 

 siderable proportion of the higher land-animals, especially carnivores 

 and ungulates, found in the northern parts of America, Asia, and 

 Europe are identical, and it is evident that the duration of species 

 in those orders is not great, for very few, if any, were living in 

 Pliocene times. It is far from unprobable that formerly the great 

 land-masses were more isolated, and consequently terrestrial orga- 

 nisms, such as mammals and most terrestrial reptiles, may have 

 had far less facilities for spreading throughout the globe. The 

 extraordinary diffusion of terrestrial forms in the Upper Ci'etaceous 

 and Eocene periods may perhaps have been caused by some great 

 breaks in the continuity of the general land-area having been then 

 filled up. As plants have, as a rule, greater power of diffusion 

 than mammals, it is not surprising that the dissemination of 

 angiosperms throughout the northern hemisphere preceded that of 

 placental mammals. There is just a possibility, if higher forms of 

 terrestrial life originated in the southern hemisphere in Palaeozoic 

 and early Mesozoic times, that the origin may have been due 

 to a greater development of land in that direction, and to the 

 great land-masses being connected to the southward up to the 

 Cretaceous or Eocene i)eriod, much as they have been united to the 

 northward in the later geological epochs. 



There may even, in the Mesozoic era, when South Africa was 

 united to India via Madagascar on one side and to South America 

 on the other, especially if the Indo-Malay continent was also con- 

 nected with the Australian, have been a girdle of laud, chiefly in 

 low latitudes, round nearly three quarters of the earth's circum- 

 ference from Peru to New Zealand and the Fiji Islands ; and this 



