RAMBLES OF A GEOLOGIST. 319 



exhibit their scratchings and polishings, like those of the 

 higher ; but wherever these scratchings and polishings oc- 

 curred in the inferior zones, no thick protecting stratum of 

 boulder-clay would be found overlying them ; and, vice versa, 

 wherever in these zones there occurred thick beds of boulder- 

 clay, there would be detected on the rock beneath no scratch- 

 ings and polishings. In order to dress the entire surface of 

 a country from the sea-line and under it to the tops of its 

 hills, and at the same time to cover up extensive portions of 

 its low-lying rocks with vast deposits of clay, it seems a ne- 

 cessary condition of the process that it should be carried on 

 piece-meal from the lower levels upwards, not from the 

 higher downwards. 



It interested me much to find, that while from one set of 

 appearances I had been inferring the gradual subsidence of 

 the land during the period of the boulder-clay, the Rev. Mr 

 Gumming of King William's College had arrived, from the 

 consideration of quite a different class of phenomena, at a si- 

 milar conclusion. " It appears to me highly probable," I 

 find him remarking, in his lately published " Isle of Man," 

 " that at the commencement of the boulder period there was 

 a gradual sinking of this area [that of the island]. Success- 

 ively, therefore, the points at different degrees of elevation 

 were brought within the influence of the sea, and exposed to 

 the rake of the tides, charged with masses of ice which had 

 been floated off from the surrounding shores, and bearing on 

 their under surfaces, mud, gravel, and fragments of hard 

 rock." Mr Gumming goes on to describe, in his volume, some 

 curious appearances, which seem to bear direct on this point, 

 in connection with a boss of a peculiarly-compounded granite, 

 which occurs in the southern part of the island, about seven 

 hundred feet over the level of the sea. There rise on the 

 western side of the boss two hills, one of which attains to 

 the elevation of nearly seven hundred, and the other of nearly 



