Land-tracts during the Secondary and Tertiary Periods, 281 



hypertropical belt of continent was continued eastward beyond 

 the Aralian region, we have not any evidence to affirm; the 

 opening-up of Central Asia will alone disclose this, and until 

 . then the limit of this extension cannot be realized ; but it should 

 not be overlooked that the great region of Oceanica, which Mr. 

 Darwin has shown to consist of submerged mountain chains of 

 immense extent, and to be now in a state of elevation and depres- 

 sion in alternate bands, is traversed by that great volcanic band 

 to the operation of which has been due the formation of the 

 major part of the Europeo- Asiatic continent, that is, the part 

 which is composed of cretaceous and tertiary formations. It is 

 to the extreme climate and widely different conditions to which 

 this configuration must have given rise, that I venture to think 

 may be attributed those complete changes in animal life which 

 took place in the intra-cretaceous and tertiary interval. The effect 

 of a continent stretching east and west, and lying in low latitudes, 

 would operate not merely to exaggerate the terrestrial heat, and 

 produce those interferences with the trade-winds which cause 

 the monsoons and bring the alternations of extreme aridity and 

 extreme moisture, but to affect the marine conditions by arrest- 

 ing the interchange of the tropical with the polar waters, — an 

 example of the effects produced by such causes being now per- 

 ceptible in the condition of the southern border of the Asiatic 

 continent, and, to a less degree, in that of Africa, where the 

 Bight of Benin washes its southern shore. 



We have seen that, as in the palaeozoic period, so in the se- 

 condary ; the complete changes in the direction of the volcanic 

 bands, which took place towards the termination of those periods 

 respectively, did not occur absolutely at their close, but rather 

 heralded it by occurring prior to the last of their epochs (as- 

 suming the Permian to be an epoch of the palaeozoic period). 

 In the former case, the changes occurred between the carboni- 

 ferous and the Permian, and in the latter we have seen that the 

 volcanic bands from east to west had come into existence, in the 

 case of the Pyrenees, prior to the formation of the upper creta- 

 ceous deposits, while the system of the Jura (which seems to 

 have originated during the cretaceous epoch, from the occurrence 

 in it of detached portions of older cretaceous beds conformable 

 to the Jurassic) possessed a direction midway between those 

 opposite ones characteristic of the secondary and tertiary periods, 

 being from N.E. to S.W. Both in the palaeozoic and secondary 

 periods, therefore, the complete changes in the fauna which 

 marked their termination do not appear to have been immediate 

 upon the changes of the geographical alignement, but to have 

 required the lapse of an epoch for their fulfilment; and the com- 

 pleteness of that change is perhaps not less the indirect result 

 Phil Mag. S. 4. Vol. 23. No. 154. April 1862. U 



