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Proceedings of the Royal Society of Edinburgh. [Sess. 
ment of drift (PL III, figs. 1 and 2). On the northern slope it forms a 
well-marked terrace (fig. 5), whose surface is about the level of the bone- 
cave. A corresponding terrace is observable about 1200 yards farther 
down the valley. No satisfactory sections of this deposit are exposed, but 
from the absence of morainic contour we infer that it represents the 
ground-moraine produced during the maximum glaciation, or at a later 
stage during the period of confluent glaciers. 
It seems reasonable to conclude that the valley of Allt nan Uamh was 
originally filled with this impervious glacial drift up to the level of the 
■caves (see dotted line a, fig. 5), so that the water entering the limestone 
was obliged to escape at the edge of the terrace where it bounded the 
limestone crag. 
A later stage in the history of the valley is indicated by the dotted 
line b (fig. 5), when the stream had removed part of the drift terrace, so 
that the water issued from the Otters’ Cave. Here the limestone appears 
at the surface through a thin covering of drift, about half-way down the 
slope (PI. II, fig. 1, O.C.). Since that period the stream has excavated 
its channel to its present level (c, fig. 5), without reaching the solid rock 
for some distance above and below the line of section. About half a mile 
farther down, however, the rocky floor is exposed where the stream issues 
from its subterranean channel (Fuaran Allt nan Uamh). Between the 
caves and the point where the Coldstream Burn reappears the bottom of 
the valley displays a succession of alluvial terraces marking stages in the 
removal of the glacial drift. 
V. Sequence of Deposits in the Creag nan Uamh Bone-Cave. 
The exploration of the most easterly cave in Creag nan Uamh yielded a 
definite succession of deposits, given below in descending order: — 
1. Peaty matter from a few inches to 1 foot in thickness. 
2. Lenticular layer of calcareous marl about 1 foot thick. 
3. Red clay or cave-earth from 1 to 3 feet in thickness, which fur- 
nished abundant remains of mammals and birds with indications of occupa- 
tion by man. 
4. Fine grey clay, about 6 inches thick, containing quartzite blocks. 
5. A bed composed of limestone fragments yielding bones of mammals 
and birds. 
6. A layer of gravel consisting of stones mostly foreign to the cave. 
A careful consideration of the evidence has led us to the following 
conclusions regarding the significance of these deposits, which are discussed 
in sequence, beginning with the oldest (fig. 6). 
