210 CRITIQUES AND ADDRESSES. ( ix. 



mentation into the form of a connected hypothetical 

 view of the manner in which the distribution of living 

 and extinct animals has been brought about. 



I conceive that distinct provinces of the distribution 

 of terrestrial life have existed since the earliest period at 

 which that life is recorded, and possibly much earlier ; 

 and I suppose, with Mr. Darwin, that the progress of 

 modification of terrestrial forms is more rapid in areas 

 of elevation than in areas of depression. I take it to be 

 certain that Labyrinthodont Amphibia existed in the 

 distributional province which included the dry land 

 depressed during the Carboniferous epoch ; and I con- 

 ceive that, in some other distributional provinces of that 

 day, which remained in the condition of stationary or of 

 increasing dry land, the various types of the terrestrial 

 Sauropsida and of the Mammalia were gradually 

 developing. 



The Permian epoch marks the commencement of a 

 new movement of upheaval in our area, which attained 

 its maximum in the Triassic epoch, when dry land existed 

 in North America, Europe, Asia, and Africa, as it does 

 now. Into this great new continental area the Mammals, 

 Birds, and Eeptiles developed during the Palaeozoic epoch 

 spread, and formed the great Triassic Arctogseal province. 

 But, at the end of the Triassic period, the movement of 

 depression recommenced in our area, though it was 

 doubtless balanced by elevation elsewhere ; modification 

 and development, checked in the one province, went on 

 in that " elsewhere ; " and the chief forms of Mammals, 

 Birds, and Eeptiles, as we know them, were evolved and 

 peopled the Mesozoic continent. I conceive Australia to 

 have become separated from the continent as early as the 

 end of the Triassic epoch, or not much later. The Meso- 

 zoic continent must, I conceive, have lain to the east, 

 about the shores of the North Pacific and Indian Oceans 



