40 Ice Marks in NortK Wales. [Jan., 



times passing over lateral spurs or rocky eminences, so during its 

 retreat the ice-cliff which terminates it will pass over each of these 

 in succession, and will deposit on many of them some of the blocks 

 which form its moraines or the boulders it has brought down with 

 it. When the glacier has finally retreated, many of these blocks and 

 boulders will remain in positions where neither simple gravitation 

 nor the action of floods of water, nor the shocks of earthquakes 

 could have placed them. Yery similar phenomena have been pro- 

 duced by the icebergs which deposited the drift, large masses of 

 rock having been carried and dropped on eminences as well as in 

 valleys. Not unfrequently these blocks rest upon rock of a different 

 kind from that of which they are themselves composed, and they 

 often rest on ice-worn surfaces marked by grooves and scratches, 

 showing plainly that the face of the country has undergone little or 

 no change since the ice left it. Many of them occur on the edge of 

 precipices and ravines, as is particularly the case at the torrent walk 

 near Dolgelly, the sides of which on nearly level ground are thickly 

 strewn with large angular blocks and boulders. One of these is 

 15 feet square and 9 feet high, and has lower ground all around it. 

 It is when they stand upon the summit of conspicuous eminences, as 

 they often do about Snowdon and Cader Idris, that they attract most 

 attention, while when thickly strewn over level ground or on slight 

 hillocks and ridges they are passed over by the tourist as too common 

 a phenomenon of mountainous countries to deserve attention. Yet 

 it is really as difficult to account for their presence in the one case 

 as in the other, without the agency of ice. Neither do they form a 

 universal feature of mountainous regions, as many suppose, for, as 

 far as my memory serves me, they do not occur on mountains of 

 moderate heights in the tropics. I have ascended many mountains 

 in the Malayan Archipelago about the same height as Snowdon, 

 and on calling to mind all the places where large blocks of rock 

 were scattered about, I cannot remember any that were not at the 

 foot of steep declivities to which they might easily have rolled. I 

 much regret that I was not then aware of the importance of minute 

 observations of the kind. It appears certain, however, that in hot 

 countries and where there is no reason to believe that glaciers have 

 ever existed, this phenomenon of the wide distribution of angular 

 blocks of rock over slight slopes, level ground, and eminences, does 

 not occur, otherwise it would have been brought forward long ago, 

 as a complete disproof of the glacial hypothesis. In South America, 

 however, I did meet with one remarkable perched block, a tabular 

 mass from 20 to 30 feet in diameter supported on two points of 

 rock only, and as far as I can recollect situated on a slight eminence, 

 certainly not under a steep slope from which it could have fallen. 

 Its position was exactly such as might be produced if it had been 

 deposited 'by a grounded iceberg, but hardly by any other means. 



