J. E. Marr and E. S. Adie — The Lakes of Snoiodon. 57 



seem that the colouring is not caused by the presence of this sub- 

 stance. The same may be said concerning the waters of Glaslyu 

 and Llyn Llydaw, which have also yielded no trace of copper. 



Cwm-glas is the next hollow which contains lakelets, and these 

 have been specially noticed by Mr. Watts. He states that there can 

 be little doubt that the upper lakelet " is a portion of a bending 

 valley dammed at both ends by scree- and stream-debris, and thus 

 compelled to find an escape over the rocky side"; and that in the 

 rainy season the lakelet finds "a second outlet over the long, low 

 col to the east, so that in this state it has the two outlets depicted 

 in the six-inch map." We here find a missing link in the series 

 of lakes leading up to those whose outlet is permanently over solid 

 rock. One of us has described Hard Tarn on Helvellyn, a lakelet 

 which strikingly recalls this tiny lakelet on Snowdon, being, like 

 it, situated on a shelf formed by a dip slope between two escarpments 

 (Quart. Journ. Geol. Soc, vol. lii, p. 13). In the Helvellyn pond, 

 the normal outlet is over drift, whilst the wet-weather outlet is over 

 solid rock ; in the Cwm-glas pool, the normal outlet is over solid 

 rock, and the wet- weather one over drift, for the drift has accumu- 

 lated to a greater extent than that at the end of Hard Tarn. The 

 next stage in the Cwm-glas pool will be the complete stoppage of the 

 eastern exit over the drift, when the pool will drain permanently 

 and in all weathers over the solid rock. 



The lower pool of Cwm-glas is stated by Mr. Watts to be 

 "certainly confined in a rock- basin, as rock occurs at its actual 

 outlet, and at every point where any former outlet might have 

 been possible. The lake is, however, so shallow that its occurrence 

 iu a basin of rock is perhaps of little consequence." We had 

 hoped to obtain soundings of this lake, but owing to the quantity 

 of floating ice, were unable to do so, although as the bottom 

 is everywhere visible, there is probably no spot where the depth 

 reaches six feet. We could not satisfy ourselves that the pool 

 occupied a true rock-basin. The stream issues from the lake with 

 a bank of solid rock at each side, but the stream is some feet in 

 width here, and its floor strewn with boulders, and a former ravine 

 six or more feet in depth might readily be blocked by detritus 

 at this point. We do not, however, believe that this is the case, for 

 just east of the present exit a drift-filled depression is seen, which 

 runs parallel to the existing stream, and joins it about 150 yards 

 below the exit, at a level far below that of the lakelet. The col 

 in this drift-filled depression is about 15 yards north of the exit, and 

 there we found a width of about five yards across from obviously 

 live rock on either side. It is true tliat large blocks of stone here 

 extend right across, but they do not seem to be in situ, for the 

 cleavage planes run in very dilierent directions in the different 

 blocks. It was easy to bury a walking-stick up to the handle 

 at several points along this depression, and iu other cases the stick 

 was prevented from ptmetrating by coming in contact with obvious 

 boulders which were movable. This pool, like the upper one, is 

 situated on a dip slope shelf between two escarpments, and the ice 



