84 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 17, 



meet the level of the sea about the latitude of the northern part of 

 Scotland. In all higher latitudes the surface of the earth would be 

 covered with perpetual snow. 



It follows, then, that if the Atlantic were converted into dry land, 

 it would still be necessary, in order to obtain glaciers to the extent 

 required by observed phsenomena, that the western part of Europe 

 should be elevated into a range extending nearlj^ from the 40th to 

 the 60th parallel of latitude, and higher than the present surface by 

 some 4000 or 5000 feet. 



26. I now proceed to that which I consider by far the most im- 

 portant of our hypothetical cases, — that in which we assume the 

 absence of the Gulf-stream and the submergence of a large portion of 

 northern and central Europe beneath the ocean. There is no diffi- 

 culty in this case in accounting for the existence of glaciers in the 

 northern parts of Scotland and in more northern latitudes ; but it is 

 necessary to consider carefully how far the conditions of their exist- 

 ence in the more southern latitudes in which traces of glacial phse- 

 nomena are observed, could be fulfilled. I will first consider the 

 Snowdonian region. 



Let us suppose Snowdon and the surrounding country lowered 500 

 feet below its present level. If the whole of Europe were depressed 

 to the same amount, a large portion of it would be submerged beneath 

 the ocean ; but we are at liberty to suppose any part of it depressed 

 to a greater amount, if necessary to produce the more complete sub- 

 mergence here assumed. I have estimated the most probable mean 

 annual temperature of Snowdon at 39° or 40° F., in the absence of 

 the Gulf-stream (art. 13, p. 68) and of any cold current from the 

 north ; and I have also shown that it would be little altered by the 

 submergence of Europe beneath the sea (art. 18, p. 75). This would 

 give the height of the line of 32° F. equal to at least 2200 feet, or 

 about 800 feet below the summit of Snowdon in its depressed position. 

 In estimating the position of the snow-line with reference to the line 

 of 32° F., it must be recollected that the region about Snowdon 

 would form a group of small islands in the midst of an extensive 

 ocean, and would so far be under conditions favourable for producing 

 a moist climate and a low position of the snow-line relatively to the 

 line of 32° F. I have already (art. 18) referred to Iceland and the 

 island of S. Georgia as furnishing cases similar in conditions to this 

 hypothetical case of Snowdon. Their insular positions and mean annual 

 temperatures are nearly the same as in that case. The difference of 

 summer and winter temperature, however, would be greater for Snow- 

 don than for either of the other cases, being about 14° for S. Georgia, 

 20° for Iceland, and between 30° and 40° for Snowdon. These con- 

 siderations would lead us to conclude that the height of the snow-line, 

 with reference to the line of 32° F., would be somewhat higher on 

 Snowdon than in the other two cases. The height of Snsefell Jokul, 

 on the north-west coast of Iceland, is, according to Mackenzie, 4558 

 feet, and that of the snow-line upon it 2734 feet, as measured by Sir 

 J. T. Stanley. The mean annual temperature there is about 38°, 

 and consequently the height of the line of 32° must be about 2000 



