124 Si)' H. H. Soivorth — Erratic Boulders in Drift. 



myself and perhaps to others, the attribution of the surface-beds to 

 such an origin is irrational and impossible (irrational because the 

 theory involves our overlooking nearly every feature of these beds 

 in order that wq may explain one or two difficulties in them ; and 

 impossible because, so far as ice can be judged by the tests of 

 ordinary mechanics, it is incapable of performing the kind of work 

 which has been demanded of it by those who explain these beds by 

 the intervention of ice in any form) — I will now turn to one 

 element in the beds which still remains to be examined, namely, 

 the foreign stones. These, as I have said before, constitute barely 

 a hundredth part of the whole, and yet they have dominated the 

 position so much that it is chiefly on their account that geology has 

 been burdened with perhaps the most stupendous appeal to the 

 imagination which it has had to carry in its long career. 



Before I turn to the special features which mark these foreign 

 stones, I will say somethuig of certain characteristics which they 

 share with all the boulders and masses of stone in these beds, and 

 which seem to put an appeal to ice for their explanation out 

 of court. 



If I traverse in part some elementary ground, it is because 

 elementary mechanics are so constantly ignored by the Glacialists. 

 By ice I mean, of course, what every-day people mean by ice — the 

 ice we can examine in our laboratories, or in glaciers, or in those 

 sheets which occupy some upland districts of Switzerland, Norway, 

 or Greenland. I do not mean the ice that exists in Mars or in 

 Saturn, or in the imagination of that transcendental school of 

 jDhilosophers who call themselves Glacial Geologists. About this 

 latter kind of ice I know nothing, and I profess to know nothing. 

 Nay, more, when I am gravely told that the ice in the ice-sheets of 

 former days was something so different to the ice we can experiment 

 upon, that it is no use appealing to the latter (which is the last ditch 

 in which the Glacialist plants himself), I feel that the question at 

 that stage has become one of poetry, and that the Poet Laureate, and 

 not a simple reader of the Geological Magazine, must be the judge. 

 The ice I propose to discuss is perlectly mundane — is frozen water 

 and nothing more. 



A glacier, such as we know it, is a mass of ice which moves to 

 some extent en masse, so long as its bed has a sufficient slope to give 

 it impetus, but in the main moves as a plastic body by the rolling of 

 one of its layers over another. 



When there are overhanging or projecting rocks above its surface, 

 these get disintegrated by the action of frost and weather, and the 

 result is that angular masses of varying size roll down upon the 

 back of the glacier. If the slope of the glacier's bed be sliglit and 

 continuous, the glacier will be a continuous river of ice, without 

 cracks and crevasses, and these angular stones will be carried by the 

 glacier on its back as far as the ice continues to move, retaining 

 their angularity throughout, and remaining angular at the finish. 



If the slope of the bed of the glacier be neither continuous nor 

 even, but be in some places at a sharp angle and in others at an 



