1916-17.] The Bone-Cave in the Valley of Allt nan Uamh. 337 
that this underground river, which is not visibly connected with any 
surface stream, may be the source of the accession to the Traligill river 
below its point of issue from the subterranean channel. 
Loch Maol a’ Choire, a small sheet of water, situated on the limestone 
plateau about three-quarters -of a mile south from the Traligill river (see 
map, fig. 1, p. 329), is now almost a closed basin. The rocks are concealed 
by the surrounding peat, but from the available evidence it would appear 
that the loch is probably floored with fucoid-beds and serpulite-grit, and 
perhaps partly with glacial material. A dry channel connecting this loch 
with the Traligill is traceable on the surface of the ground, evidently 
representing an old stream course carved by the water issuing from the 
lake. In the lower part of this channel occurs a cave (Uamh Cailliche 
Pearag) which forms a tunnel with an aperture up stream. It is clear 
that the water at one time entered this chimney, flowed out of the tunnel, 
and pursued its course above ground till it joined the Traligill. 
Throughout the limestone plateau the most striking example of the 
disappearance and reappearance of a stream is furnished by the Allt nan 
Uamh or Coldstream Burn. It rises near the crest of the Breabag range 
above the 2000-feet contour-line (fig. 1, p. 329), descends the quartzite slopes, 
and, soon after reaching the limestone belt, plunges beneath the surface, 
and runs underground for a distance of about a mile. It reappears as a 
powerful spring (Fuaran Allt nan Uamh, spring of the Burn of the Caves), 
about half a mile above the junction of the Coldstream Burn with the 
Loanan river. In periods of excessive rainfall or rapid melting of snow 
in the upper part of the catchment basin, when the volume of water is 
too large for the subterranean channel, the swollen stream reverts to its 
old water-course. But under normal conditions the channel remains dry 
for about a mile above the Fuaran Allt nan Uamh. 
IV. Relation of the Creag nan Uamh Bone-Cave to the Glacial 
Deposits in the Valley of Allt nan Uamh. 
About a mile and a quarter up Allt nan Uamh from its point of 
junction with the Loanan river, a prominent crag of Eilean Dubh lime- 
stone (named on the 6-inch map Creag nan Uamh, Crag of the Caves) 
appears on the south side of the valley at a height of about 150 to 200 
feet above the dry channel of the stream. The bone-cave is the most 
easterly of three caves at the base of this crag (PI. II, fig. 1). The steep 
slope between the caves and the stream course is composed of highly 
denuded glacial drift, partly covered with scree material (PI. II, fig. 1). 
On both sides of the valley at this point there is a considerable develop- 
vol. xxxvii. 22 
