532 HENEY F. BLANFOKD ON THE 



long. But such a mountain-range would offer an obstruction to the 

 passage of the winds, such as would certainly diminish their volume ; 

 and it may be questioned whether the total precipitation would be 

 greater than it now is. Some extension of the glaciers would pro- 

 bably result were the quantity of vapour brought to these mountains 

 much greater than is now brought ; and there may have been some 

 increase when, as Mr. W. T. Blanford has shown*, the present 

 deserts of Baluchistan and Persia were occupied by great inland seas 

 or lakes, and when, therefore, the westerly winds were damper than 

 they now are. But in the case of the Sikkim Himalaya the outer 

 slopes now receive some of the heaviest rainfall in the world f, yet 

 the glaciers of the snowy chain do not descend below 14,000 feet. 

 Even, then, if the assumed former elevation of the Himalaya were 

 less purely hypothetical than I think it is, it seems inadequate to 

 explain the glacier phenomena of these mountains, and it would 

 have little or no application in the case of the Naga Hills, which 

 form no part of the Himalaya. 



If this solution of the problem be rejected, there remains the 

 supposition that the temperature of the whole region was formerly 

 very much lower than that which now prevails. The Mer de Glace, 

 in the Western Alps, descends to 4000 feet, this part of the Alps 

 being situated about on the isotherm of 55°. Sibsagar, in the 

 Asam valley, north of the Naga hills, is on the isotherm of 75° -5. 

 To produce glaciers that should reach down to 4500 feet in these 

 hills, we should then require a diminution of nearly 20 degrees in the 

 mean annual temperature ; and at least an equal reduction would be 

 necessary to prolong the glaciers of the Sutlej basin down to 2000 

 feet, or even 3000 feet. I am unable to conceive any change of 

 the local physical geography, consistent with the existence of the 

 Himalayan chain, which should induce such a revolution of the 

 climate as is here required. The theory of Mr. Croll seems to me 

 equally inadequate, since the change in the mean annual tempera- 

 ture which, on his showing, might result from the varying eccen- 

 tricity of the earth's orbit and the precession of the equinoxes, 

 must diminish rapidly in low latitudes, becoming zero at the equator. 

 Moreover, if the glacial phenomena of Patagonia, described by Mr. 

 Darwin, are to be assigned even approximately to the same period 

 as those of Europe (which, if not proved, has certainly not been 

 disproved), his theory would, as I understand it, necessarily fail to 

 account for the phenomena. 



The questions of terrestrial physics involved in this inquiry are 

 too vast and complicated to be entered upon here ; and it cannot 

 perhaps be determined on the present evidence whether the diminu- 

 tion of temperature during the glacial period affected one hemisphere 

 only, or both simultaneously.. But in the present state of the ques- 

 tion it seems to me that such hypotheses as have been put forward 



* Quart. Journ. Geol. Soc. vol. xxix. p. 493. 



t At Buxa fort, north of Groalpara, the average of four years was 256 inches. 

 At Rangbi, within the hills of Sikkim, that of six years was 175 inches ; and at 

 Darjiling that of ten to thirteen years was 125 inches. 



