194 HIS GRACE THE DUKE OF ARGYLL, K.G., K.T., ON 



called, which moved upon, and moved over all the hills, in enormous masses, and there- 

 fore with an enormous pressure universally applied. The marks appear to me to be 

 incompatible with any such supposition. They are essentially partial, local, and what 

 may be called selective. We cannot attribute this partiality to the disturbing effects of 

 subsequent obliteration ; because the same rock in the same place which is highly glaciated 

 on some one part of its surface is wholly untouched upon other parts. Some rock 

 surfaces, indeed, do exist, which have been evidently wholly covered by, and ground 

 down under enormous and continuous moving pressure into one smoothed and polished 

 Moor or dome, and these rocks are of the greatest interest in showing to us what 

 the characteristic effects of such an agency must always be. But though they exist, they 

 are comparatively rare. For every one specimen of this kind of glaciation there are 

 hundreds of thousands in which the smoothing, abrading, or scratching agency has acted 

 on some one side of a rocky surface and has left the other side rough and untouched. 

 There is, however, one general rule or law which can be clearly traced. The direction 

 from which the agency came, and the direction towards which it moved, is almost always 

 determined by the existing configuration of the land, — that is to say, rocks on the sea- 

 shore have been smoothed by some body which must have moved along the coast from 

 the higher hills towards the lower ranges, or towards the outlets of the arms of the sea 

 on which they are abundant. In like manner, in the glens not occupied by water, they 

 follow the lines of the glen from its head towards its opening. So far, this is easily 

 intelligible, because, if the configuration of the country was substantially what it is now, 

 ice moving in the form of ordinary glaciers, such as those of Switzerland, would, and 

 must, be guided in their course by the direction of the hollows in which they lie, or, if 

 moving in the form of floating or floe-ice, would equally be guided by currents similarly 

 determined. But there is this difference to be noted, that even small glaciers, such 

 as those which we now have on the Alps, do produce surfaces wholly polished upon those 

 particular rocks over which they actually move in a solid mass. Very partial glaciation, 

 therefore, such as leaves large parts of a rock wholly untouched, cannot indicate the 

 passage of ice in this particular form, whilst it is not only consistent with, but character- 

 istic of ice floating in water, and made by currents to impinge upon rocks which interrupt 

 its passage. The floating masses grate along the shores, or the rocks which constitute a 

 shore for the time being — catching the projecting surfaces as they pass, and necessarily 

 leaving untouched the retired or sheltered surfaces, which do not obstruct the way. 

 Then there is one phenomenon, which clearly indicates the same agency — although under 

 the same conditions, which startle us not a little — and that is the glaciation of rock 

 surfaces which constitute the summits of high hills, far above the general level of the 

 whole country, and not situated in any glen or hollow which could possibly have guided 

 either a solid glacier or a mere shore current. These glaciated tops are often smoothed 

 or striated on one surface only — with a sheltered side as rough and as well-marked as any 

 similar rock upon the existing shores. This is quite inconsistent with the passage of 

 that enormous kind of glacier which is denoted under the name of an Ice Sheet or an Ice 



