Change of Climate during Geological Epochs. 135 



height of summer, be almost wholly covered with frozen snow, 

 in some places many fathoms deep. . . . The head of the bay was 

 terminated by ice-clifts of considerable height ; pieces of which 

 were continually breaking off, which made a noise like a cannon. 

 Nor were the interior parts of the country less horrible. The 

 savage rocks raised their lofty summits till lost in the clouds, 

 and valleys were covered with seemingly perpetual snow. Not 

 a tree nor a shrub of any size were to be seen. The only signs 

 of vegetation were a strong-bladed grass, growing in tufts, wild 

 burnet, and a plant-like moss, seen on the rocks. . . . We are 

 inclined to think that the interior parts, on account of their ele- 

 vation, never enjoy heat enough to melt the snow in such quan- 

 tities as to produce a river, nor did we find even a stream of 

 fresh water on the whole coast"*. 



This rigorous climate chiefly results from the rays of the sun 

 being intercepted by the dense fogs which envelope the island 

 during the entire summer; and the fogs, again, are due to the 

 air being chilled by the presence of the snow-clad mountains, 

 and the immense masses of floating ice which come from the 

 antarctic seas. A reduction of one-fifth in the amount of heat 

 received from the sun during winter would, in this country, 

 produce a state of things as bad as, if not worse than that which 

 at present exists in South Georgia. 



Some may be apt to suppose that the presence of the Gulf- 

 stream would under such a condition still prevent our British 

 seas from freezing during winter. We may, however, remark 

 that it is not necessary for us to assume that our seas were frozen 

 during the glacial epoch. We know that the seas around Sand- 

 wich Land, and the island of South Georgia, are never frozen, 

 and yet the perpetual snow descends to a lower level than it does 

 in Greenland or in Spitzbergen. All that seems necessary would 

 be the presence of immense masses of floating ice during summer 

 months, and this we should then no doubt certainly have, not- 

 withstanding the presence of the Gulf-stream. 



But if we examine the matter fully, we shall find that the 

 Gulf-stream as well as the climate is affected by the change in 

 the excentricity of the earths orbit. 



It is now generally admitted that the cause of the great oceanic 

 currents is the constant impulse of the trade-winds on the sur- 

 face of the ocean. The trade-winds, on the other hand, owe their 

 existence to the difference of temperature between the equatorial 

 and polar regions of the globe. Now any cause which tends to 

 increase or diminish this difference will, other things being 

 equal, tend also to increase or diminish the strength of these 

 aerial currents. The general tendency of the under currents of 

 * Capt. Cook's Second Voyage, vol. ii. pp. 232, 235. 



