318 KAMBLES OF A GEOLOGIST. 



of subsidence is of a character tolerably satisfactory. The 

 dressed surfaces occur in Scotland, most certainly, as I have 

 already stated on the authority of Dr Fleming, at the height 

 of fourteen hundred feet over the present sea-level ; it has 

 been even said, at fully twice that height, on the lofty flanks 

 of Schehallion, a statement, however, which I have had 

 hitherto no opportunity of verifying. They may be found, 

 too, equally well marked, under the existing high-water line ; 

 and it is obviously impossible that the dressing process could 

 have been going on at the higher and lower levels at the same 

 time. When the icebergs were grating along the more ele- 

 vated rocks, the low-lying ones must have been buried under 

 from three to seven hundred fathoms of water, a depth from 

 three to seven times greater, be it remembered, than that at 

 which the most ponderous iceberg could possibly have ground- 

 ed, or have in any degree affected the bottom. The dressing 

 process, then, must have been a bit-and-bit process, carried 

 on during either a period of elevation, in which the rising 

 land was subjected, zone after zone, to the sweep of the armed 

 ice from its higher levels downwards^ or during a period of 

 subsidence, in which it was subjected to the ice, zone after 

 zone, from its lower levels upwards. And that it was the 

 lower, not the higher levels, that were first dressed, appears 

 evident from the circumstance, that though on these lower 

 levels we find the rocks covered up by continuous beds of the 

 boulder-clay, varying generally from twenty to a hundred feet 

 in thickness, they are, notwithstanding, as completely dressed 

 under the clay as on the heights above. Had it been a rising 

 land that was subjected to the attrition of the icebergs, the 

 debris and dressiags orthe higher rocks would have protect- 

 ed the lower from the attrition ; and so the thick accumula- 

 tion of boulder-clay which overlies the old coast line, for in- 

 stance, would have rested, not on dressed, but on undressed 

 surfaces. The barer rocks of the lower levels might of course 



