EEMARKS ON GLEIT EOT. 25 



detritus, containiBg many angular pieces of rock from 2 to 3 and 

 perhaps in some cases 4 feet in diameter. This shades off upwards 

 into coarse detritus with fewer large fragments, but the stony debris 

 only partially waterworn, while the uppermost part of all is rather 

 finer and more silty. Stratification lines are scarcely visible in this 

 section, which was the clearest one I saw." This bank fills up all 

 the side of the glen and extends up the Turret to the level of the 

 lowest parallel, presenting to the Eoy a steep front which I roughly 

 measured and found to rise about 90 feet above the level of that 

 stream at its base. The general character of the surface is very flat, 

 and corresponds with the part measured, but in some places rises 

 above it. The Turret has cut its way through the bank, and a little 

 farther up has carried away a good deal of its mass. 



I have no doubt that the laminated silty portion at the base must 

 have been hidden at the time of Prof. Prestwich's visit by the 

 slipping down of stuff from above, for his description corresponds 

 with the middle part of the bank. It is quite possible there may 

 be some old moraine matter enveloped in the interior of this large 

 bank of stuff, for it is of great extent, but the laminated silty cha- 

 racter of its base and the general flatness of its surface (as may be 

 seen from Prof. Prestwich's own view of it and also from plate xv. 

 in MacCulloch's memoir) are against the notion of its being formed 

 by a glacier. 



Prestwich further objects that it cannot be a delta because " the 

 accumulation of the main mass is at the most remote instead of the 

 nearest point of discharge." But is not this one of the characteristic 

 features of a delta, and is it not implied indeed in its very name? 

 Another objection is that there is no " sorting of its materials from 

 its head at the Turret Pass to its extremity on the Eoy." But this 

 is just what we do not know, for there is an absence of any clear 

 section to instruct us in regard to this point. We have also to re- 

 member that we have to do with a glacial climate when there would 

 be much ice in the waters and the margin of the lake would be often 

 frozen, and further that the spot is surrounded by steep hills down 

 which the streamlets in time of flood descend with considerable force. 

 Moreover, when the lake sank from the highest to the middle line, 

 and again from that to the lowest, there would be a sweep of water 

 amply sufficient to move large stones, and perhaps this explains the 

 rough character of the middle zone of the delta. The abnormal size 

 of the deposit is no doubt due in some measure to the overflow of the 

 Glen Gluoy lake having contributed to its formation, as I mentioned 

 in my previous paper. 



Again, Prof. Prestwich objects that its surface is not an inclined 

 plane, but to me it appears to approach this as nearly as we could 

 expect in an old worn delta over and through which the Turret had 

 to cut its way. Prof. Prestwich's opinion about these deltas is 

 opposed to that of MacCulloch, Darwin, Chambers, Milne-Home, 

 Lubbock — in fact almost every one who has noticed them. 



Owing, no doubt, to some ambiguity in my language Prof. 

 Prestwich has misapprehended what I iSaid about the height of the 



