ANOTHER POSSIBLE CAUSE OF THE GLACIAL EPOCH. 153 



Without going further into this veiy interesting subject, 

 which I have dealt Avith in a former communication to this 

 Institute,* it must here suffice to state that owing to the 

 uprise of the whole region to the extent of 1,200 to 1,500 

 feet (200 to 250 fathoms) large tracts now under water were 

 converted into land, and the adjoining land areas were up- 

 raised. This uprising of the land necessarily brought certain 

 mountainous tracts within the limits of the snow line — as 

 was the case in the Lebanon — where, as Sir J. U. Hooker has 

 shown, glaciers were formed which have left their old 

 moraines at a level of 4,000 feet above the present surface 

 of the Mediterranean ; mountainous regions such as the 

 Caucasus, where perennial snow lies, were subjected to a 

 more rigorous climate. That this general elevation of the 

 Mediterranean and Syi-ian region extended much farther 

 eastward I cannot doubt ; how far it is impossible to say ; 

 but there does not appear to be any reason why its influence 

 may not have been felt as far as the Himalayas, where, as we 

 know from the observations of Sir J. D. Hooker, the glaciers 

 once descended far below their present limits.f In all these 

 considerations v/e must remember that the two possible 

 causes — those of reduced temperature and of land elevation 

 — were acting simultaneously ; and it is to their combined 

 influence that I venture to ascribe the general lowering of 

 temperature, and prevalence of more Arctic climatic con- 

 ditions of which we have evidence during the Pleistocene 

 period. 



Part IV. — Conclusion. 



The causes which have been assigned for a glacial epoch 

 may be arranged under two heads — the astronomical and 

 the terrestrial. Under the former may be placed the theory 

 of the late Dr. Croll, which has the support of Prof. James 

 Greikie, and that of Sir Robert Ball more recently enun- 

 ciated ; imder the latter is that of Lyell, who held that " in 

 determining the climate of the globe geographical changes 

 have exercised a preponderating influence."! Croll's hypo- 

 thesis has been examined by Lyell, Prestwich,§ and others, 

 who are unable to accept its conclusions, as well on astro- 

 nomical as on physical grounds. Lyell in the last edition of 



* Trails. Vict. Inst., vol. xxix (1895). 



t Hookei', Himalayan Journals., vols, i and ii (1855). 



\ Principles, vol. i, ch. 12. ^ Geology, vol. ii, p. 528. 



