1867.] Ice Marks in North Wales. 47 



although very few of us may be able to form any sound judgment 

 as to what angle will stop a glacier's motion up hill. 



It would appear, then, that there is at all events a strong case 

 in favour of glaciers having had something to do with the formation 

 of lakes. I therefore examined with much interest into the peculiar 

 arrangement and position of the small lakes of North Wales, to see 

 if they gave any support to Professor Kamsay's theory or seemed 

 inconsistent with it. We may conveniently group most of these 

 lakes into: — 1st, such as lie in more or less regular bowl-shaped 

 hollows of the mountains ; and 2nd, those situated in longitudinal 

 valleys. Immediately beneath the peak of Snowdon are three great 

 chasms, which contain small lakes at an average elevation of 

 2,000 feet above the sea. On the east is Grlas llyn, on the north 

 are the two small lakes of Cwm glas, and on the west are the 

 three little lakes of Cwm Clogwyn. All these he in irregularly 

 bowl-shaped valleys with a comparatively narrow opening ; they all 

 spread out and are larger within than the entrance to them would 

 lead one to expect. Another feature they have in common is a 

 comparative flatness of bottom. From below you have to climb a 

 steep ascent or even a precipice to reach them, but when you have 

 surmounted this you find a rugged undulating surface spreading 

 out to the foot of the precipices which every where surround it. 

 Cader Idris has two somewhat similar chasms containing lakes, and 

 on carefully examining the Ordnance maps we see that there are 

 numbers of such lakes around the higher mountains, occupying 

 lofty bowl-shaped chasms with a more or less narrow exit. One of 

 the largest of this class of lakes is Llyn Llydaw, which is more 

 than a mile long and lies right across between two spurs of Snowdon, 

 which close round it so as to leave a very narrow entrance. How 

 these valleys were originally formed it is not very easy to understand, 

 unless they can be connected with varying texture and resistance of 

 the rocks. The symmetry of their arrangement around or on each 

 side of lofty mountains is against this supposition, and I have been 

 often inclined to think that they must owe their peculiar form to 

 marine action during the various submergences the country has 

 undergone. However this may be, it is evident that such a form 

 of ground being already in existence when the glacial period, came 

 on, the ice must have accumulated in these crater-like hollows to a 

 great height, and pressing forcibly on a nearly flat or undulated 

 bottom while in slow but continued motion outwards, could hardly 

 fail to deepen the basin here and there and thus form the little 

 lakes we now see. 



The second class of lakes or those in longitudinal valleys are 

 generally situated at a much lower level, and are as a rule larger 

 than the mountain tarns just described. The two lakes of Llanberis, 



