1867.] Ice Marls in North Wales. 37 



its terminal ice-cliff has successively occupied ; when on the other 

 hand it is stationary for a considerable time, the debris accumulates to 

 some height, and forms a well-defined terminal moraine. Some of 

 the moraines formed by the old Swiss glaciers, when they stretched 

 iar down into the plains, are enormous. That of Ivrea in North 

 Italy is many miles in extent, and 1,500 feet high — a mountain of 

 debris brought down by a glacier which was sixty miles long. 

 There is no other natural agent which can form on level ground 

 such regular mounds as these moraines, many of which resemble 

 artificial earthworks. Their presence becomes therefore a very 

 certain indication of the former existence of glaciers. 



In North Wales many very perfect moraines may be observed. 

 Around Snowdon in particular they are very abundant, every one 

 of the valleys which radiate from the central peak of the mountain 

 exhibiting them more or less distinctly. These are all described in 

 Professor Ramsay's little work on the Old Glaciers of Switzerland and 

 North Wales ; and I can bear witness that, far from exaggerating, 

 he has hardly dwelt sufficiently on the wonderful clearness and 

 well-marked character of this phenomenon. The most striking of 

 all are perhaps those of the Cwm Glass Valley, which descends from 

 the north of Snowdon to the pass of Llanberis. At the mouth of 

 this valley, close above the road which ascends the pass, is what 

 seems to the passer-by a steep rocky hill, but on viewing it from an 

 elevation about a quarter of a mile lower down, it is seen to be a 

 huge longitudinal roof-shaped mound of almost perfect regularity, 

 scattered over with angular blocks of rock ; and whose position, with 

 regard to the sides and bottom of the valley, shows it to be an 

 addition — something put there — and having no relation to the 

 proper contours of the surface. Higher up the valley is a small 

 but wonderfully perfect moraine, which stretches across in a regular 

 curve, and of almost uniform size and height, so that when standing 

 on it one can hardly help believing it to be an artificial fortification. 

 But the huge angular blocks of rocks scattered about it, and the 

 other signs of ice-work all around, with the wild loneliness of~the 

 situation, and its inferiority as a defensive position to many other 

 points near it, utterly forbid this supposition. The best example of 

 the wide-spreading of rocky debris by the gradual retreat of a 

 glacier, is to be seen in Cwm Brwynog. Under one of the blackest 

 precipices of Snowdon lies the little green lake Llyn dur Arddu, on 

 the other side of which rises a steep ridge, most likely partly rock 

 and partly moraine. Beyond this ridge extends for nearly a mile 

 a gradually-sloping upland, so thickly covered with blocks of rock, 

 often of large size, that from a distance the hsrbage can rarely be 

 seen between them. In this case every one of these rocks must 

 have been carried across the valley of the lake and deposited where 

 it now lies, and no other natural agent can be found or imagined 



