548 
NATURE 
[APRIL 7, 1904 
—__—— 
Loch Earn is extremely simple in conformation and flat- 
bottomed in character, the depth of water increasing 
gradually from the shores down to the deepest part, which 
is centrally placed, but rather nearer the upper (west) end. 
A depth of 100 feet is met with less than a quarter of a 
mile from the west end and less than half a mile from the 
east end. The 200-feet basin is 4} miles in length, distant 
about three-quarters of a mile from the west end and 14 
miles from the east end, while the 250-feet basin is nearly 
two miles in length, being distant 13 miles from the west 
end and 3 miles from the east end. The maximum depth 
of 287 feet was observed near the centre of the loch, between 
the mouth of the stream called Allt Bhacaidh on the 
northern shore and that of the Allt Dhtnain on the southern 
shore, about 2% and 3% miles from the west end and east 
end respectively. The areas between the consecutive con- 
tour-lines, and the percentages of the total area, are :— 
Fest Acres Per cent. 
0 to 100 926 384 
100 ,, 200 755 315 
more than 200 700 30 
2381 100 
Loch Laidon, the largest of the Rannoch Moor lochs, lies | 
on the boundary line between Perthshire and Argyllshire. 
It trends in a north-east and south-west 
direction, sending out a long shallow 
arm towards the west, and with a small 
shallow distinct basin, called Dubh 
Lochan, at its north-eastern end.’ The 
floor of the loch is rather irregular. 
The deepest part is in the centre of the 
loch, where there is a basin three- 
quarters of a mile in length and more 
than 1oo feet in depth, the maximum 
depth of 128 feet having been observed 
about 22 miles from the south-west end 
and 23 miles from the north-east end. 
Outside of this main 1oo-feet basin, 
isolated soundings of 104 and 100 feet 
were obtained to the south-west, and a 
sounding of 100 feet to the north-east. 
The principal 50-feet basin extends from 
less than a mile from the south-west end 
to less than 13 miles from the north-east 
end, and is nearly 3 miles in length; a 
smaller basin, one-third of a mile in 
length, lies in the north-eastern part of 
the loch, separated from the larger basin 
by an interval of a quarter of a mile, 
with an isolated sounding of 50 feet 
midway between them. Of the entire 
lake-floor, 74 per cent. is covered by less 
than 50 feet of water. 
Loch Tummel is the final one on the 
Tummel branch of the Tay, and it re- 
ceives the outflow from all the other 
lochs on this branch, including Lochs Ericht, Rannoch, and 
Laidon; its drainage area is thus very considerable—about 
306 square miles, or 312 times the area of the loch. It is 
irregular in outline and in the conformation of the bottom. 
The west (or inflow) end of the loch is shallow, and is 
being silted up by the large amount of alluvial matter 
brought down by the river; two large tongues of alluvium 
project into the loch on both sides of the river, and, indeed, 
the loch must formerly have extended much farther towards 
the west, but has been gradually silted up and shortened. 
Cones of alluvium have also been formed at the mouths of 
the inflowing streams, both on the northern and southern 
shores. The loch is divided into three deep basins by two 
ridges crossing the loch, the depth on the western ridge 
being 53 feet and on the eastern 56 feet, so that the 5o-feet 
area is continuous, and nearly 23 miles in length, approach- 
ing to within 100 yards from the east end and a quarter of 
a mile from the west end. Of the three deep basins, the 
western one is the deepest, with a maximum depth of 128 
feet ; the central one has a maximum depth of 119 feet, and 
the eastern one a maximum depth of gg feet. A view of 
Loch Tummel is shown in Fig. 3. The areas between the 
contour-lines, and the percentages, are :-— 
NO. 1797, VOL. 69] 
Feet Acres Per cent, 
oto) Somes 352 56 
50 ,, 100) =. 217 344 
morethaniIoo_ ... 60 94 
629 100 
Loch Garry lies to the east of Loch Ericht, and resembles 
it in trend and in outline. The 25-feet, 50-feet, and 75-feet 
areas are continuous, the 50-feet area being nearly two 
miles in length. There are two 100-feet basins, separated 
by depths of 82 to 93 feet, the larger one in the southern 
half of the loch, with a maximum depth of 105 feet, the 
smaller one in the northern half, enclosing the maximum 
depth of the loch (113 feet). The areas between the contour- 
lines, and the percentages, are :— 
Feet Acres Per cent. 
OMtOmS OMe ZOO snc: eee ee 52 
50 ,, 100 NAS). cag don 1008 43 
more than 100 TO eco es es 5 
389 100 
Loch Lyon is extremely simple in outline and in conform- 
ation. It is nearly uniform in width, except for a cone of 
alluvium laid down by the river on the south-eastern shore. 
The lower (north-eastern) end is shallow, as though it had 
Fic. 3.—Loch Tummel. 
been silted up, the 25-feet contour being distant about a 
quarter of a mile, while at the upper end the 75-feet contour 
approaches to within 300 yards of the shore. The alluvial 
cone mentioned causes a constriction in the outline of the 
loch accompanied by a slight shoaling of the water, the 
depth here being 77 feet, deepening to 84 feet to the south- 
west, and to 100 feet to the north-east; the last-mentioned 
sounding—the maximum depth observed—occurs approxi- 
mately in the middle of the loch. The areas between the 
contour-lines, and the percentages to the total area of the 
loch (which show the flat-bottomed character of the deep 
basin), are :— 
Feet Acres Per cent. 
oto 25 92 , 39 
255, 50 36 CLit) 15 
50>, 75 55°: roe 23 
more than 75 SOs ‘ 23 
236 100 
The Loch of Lintrathen is the source of the Dundee 
water-supply, and has been raised 22 feet in connection 
therewith ; Loch Turret similarly supplies the town of Crieff, 
