II

Laci barréi par dei moraines.

594 LAC DE MiERJËLIN.

lo Capel Curig ; of Gwm Elen and of Marchlyn-raawr * and Marchhih bach', in the high recess belween Elidyr-fawr and Moel Perfedii» near Ihe path from Llanberis lo Nant Francon. Judgîng by ihe présent average élévation of thèse lakes, when the moraines thatcoDfined thera were formed, the highest parts of Ihe mountain^^ of Cacrnarvonshire could not bave been more than from 1400 to 3000 feei (425 à 610 mètres) above the sea.

In those cases where ordinary terrestrial moraines form the confining barriers of mountain lakes and tarns, it is, as already stat^i, not to be supposed that the depths of thèse moraines is alwapequal to the profoundest depth of the lakes. The contrary, I venturetn say, is often the case, although I bave had no opportunily of sonir diiig Llyn Llydaw, Llyn Idwal, and several olher deep lakes , whero I believe this will be found to be true. I hâve already said , that it seems to me probable that such rock basins were ground out ty heavy loads of ice , which in their onward progress scooped dcep hollows in parts of their channels ; and this might easily be the case, when this grinding action lasted after a glacier had retîred above the position of the présent lake barrier, so that thewaste ofthirocky floor being long contînued, by degrees the glacier wore oui a dépression deeper and deeper, till on ils final retirement ihe spaiv once occupied by ice , became fiUed with the water drainage of iht valley. As in Wales , so also I believe that this was probably th^ case in the valley of the Aar, above Ihe Kirchet. It also seems probable that the same process helped to form the hollow of Ihe Mârjelen-see, on the east side of the low ridge covered by ice that seprates that valley from the deeper hellow through which Ihe Alelscb glacier descends.

L.C de iMû.jticn R. 15. This most interesting lake is bounded on the westbya "" *^7;7p,5'^'''^^ protruding portion of Ihe Great Glacier of Aletsch, ending in a cîitT

of ice, from which fleets of small icebergs frequently break. Inoldei limes a branch from the main glacier fiUed the space now occupii-^i by Ibe lake, and passing further east united the glaciers of Aletsch auJ Viesch. But a change ofclimate lessened the size of the Alpine g!a-

* Yeliow Pool or Lake.

* LitUc Rorse Pool.

LAC DE MiERJELEN. 595

ciersy the uniling siream of ice gradually melted, it shrunk upwai^ds, and ail that now remains is the projection ending in an ice-cliff, washed by tbe waters of the lake. Old moraines furrow the sides of the bounding hills , and the lower end of the lake is partially dammed by moraine matter, which, by approximate measurement, 1 foundto be abouttwenty-fîve feet (7™,60) thick from the surface of the water to the rock on nvhich it lies.

The ice touches the bottom of the lake. To ascertain its depth was a matter of spécial interest to me , as a means of comparison with some of the lakes in North Wales; and I was not at the time aware that at inlervals of eight or ten years it is drained by a temporary passage , opened through the ice of the Aletsch glacier. To souud it I borrowed a Une from Dr. TyndaU. We parted on the glacier on a fine aflernoon last August, and while he started with Bennm, the guide of the iËggischhorn lo pass the night in the cavern of the Faulberg on is way to the summit of the Finster-Aar Horn » I sel to work with line and plummet. I was assisted by Christian Lauener , the guide of Lauterbrunnen. For the first two observations he secured me by a rope passed round my waist, but growing bolder with practice, I dispensed with this safeguard during the remaining obsen'ations , and contented myself with a place eut in the ice in which to plant my foot. The work took about two hours, for the crevasses are so fréquent and broad , that it is impossible to walk straigbt along the edge of the icecliff, and we were oflen obliged to make détours to reach the points from which I wished to take the soundings. As might be expected , the lake is shallowest near the sides, and deepest near the middle, where the clifTof ice lowers till its edge is only a few feet above the water. The gréâtes t height of Ihe clilT obove water was sixty feet(18"°,2). By seven accurate soundings, I ascerlained that the depth of water by the ice-cliff varies from thirty-four to ninetyseven feet ■ (10™ ,3 à 29™,5).

It may be that this inner hollow was scooped out by ice in tbe manner above suggested.

Next day but one, I returned alone to make some further obser*

* The Température of ihe water near the ice was do Cent., and ftirther off it rose to 3« 1/2 at 6.30 P. M.