THE FRESH-WATER LOCHS OF SCOTLAND. 
49 
enclosed by the 90-feet contour-line, and the deepest sounding being 
97 feet. A fault, with a downthrow to the west, crosses the head of 
the loch at the Trossachs Hotel, which has produced considerable 
brecciation of the strata, a feature probably continued along the floor 
of the loch between the hotel and Achray. The greater part of this 
lake is on the upthrow side of the fault just referred to, and the basin, 
as already indicated, has been excavated mainly in slates. 
Loch VennacJiar . — Between Loch Achray and Loch Vennachar there 
is a strip of alluvium, the difference in level between the two lakes 
being 6 feet. The successive terraces show that these two lakes 
originally formed one sheet of water, which stood at a somewhat 
higher level. Loch Vennachar contains one prominent basin, about 
2 miles in length, enclosed by the 50-feet contour-line. Within this 
limit there are two smaller basins, which fall below the level of the 
100-feet contour-line (see Plate V.). The deepest sounding is 111 feet, 
which occurs to the north-east of Invertrossachs, on the line of the great 
boundary fault along the Highland border, which has a downthrow 
to the south-east. West of this dislocation the floor of the lake rises 
sharply to a level of 20 feet below the surface. Westwards, however, 
near Lanrick, the depth increases to 50 feet, a feature which coincides 
with the course of two faults crossing the loch — branches of the Loch 
Tay fault, and each having a similar downthrow to the west. Doubtless 
where the deep soundings coincide with lines of fault, the strata have 
been much shattered and crushed, which has led to the more rapid 
disintegration of the materials. But though these faults may have led 
to local modifications of the floor of the lake, they obviously do not 
account for the excavation of the basin. The long, narrow hollow, 
crossing obliquely these lines of dislocation, points to glacial erosion. 
Loch Drunkie . — Beference has already been made to the geological 
features of this basin (see p. 42). In the western portion of the west 
branch, where the hollow has been scooped out of slates, a small part 
of the floor is enclosed within the 50-feet contour-line. The deepest 
sounding, 97 feet, occurs in the north branch of the lake in front of a 
ridge to the east, which rises to a height of about 150 feet above the 
loch. The direction of the striae at Loch Drunkie is E. 20° S., and 
the deepest sounding is found where the erosion must have been 
greatest. 
Loch Arklet . — This lake lies across the path of the great ice-sheet, 
and coincides with the trend of the later movement (see pp. 44 and 
45). Both the north and south shores of this loch are surrounded by 
moraines, but though such is the case the stream flows over solid rock, 
where it leaves the alluvial flat 14 miles west of the outlet, and con- 
tinues to flow for half a mile over solid rock. Originally the lake must 
have extended westwards to this barrier, for the intervening strip cf 
alluvium has been laid down by the burns joining the Arklet water not 
E 
