74 
BATHYMETRICAL SURVEY OF 
55 acres, or over 23 per cent. ; and the area over 75 feet in depth is 
about 53 acres, or less than 23 per cent, of the entire area of the loch. 
The comparatively flat-bottomed character of the deep basin is indicated 
by the larger proportion of the bottom covered by water between 50 
and 75 feet in depth, as compared with the proportion covered by water 
between 25 and 50 feet, the average slope being thus considerably steeper 
in depths of 25 to 50 feet than in depths of 50 to 75 feet ; and this latter 
gentler slope is continued into the deeper water over 75 feet in depth, 
as shown by the nearly equal areas on both sides of the 75-feet line. 
The large proportion under 25 feet in depth is due to the considerable 
silted-up area towards the north-east end of the loch already referred to. 
Loch Lyon was surveyed on May 10, 1902. No bench-marks were to be 
seen along the shores, nor on the Ordnance Survey charts, but the 
height of the surface of the loch was estimated as being about 1050 feet 
above the sea. Lines of drift were observed 4 feet above the water, 
which, according to the keeper, was about its normal height at the time 
of the survey; the water rises suddenly and falls as quickly, and might 
fall perhaps a foot lower than on the date of the survey. Thus a range 
of about 5 feet in the level of the water is indicated. The temperature 
of the surface water on May 10, 1902, when commencing the survey, 
about noon, was 48°’ 7 at the edge of the bank at the north-east end, 
and readings taken along the shore gave 50°, 51°*8, 52°-5, and 58°. In 
the afternoon, readings of 47°*9 were taken in shallow water towards the 
northern shore, 48°*9 near the south-west end, and 46°-4 in, the centre 
of the loch. These observations show a range of ll°-6 in the temperature 
of the surface water throughout the day, viz. from 46°‘4 to 58°. 
Loch Dochart (see Plate XX.). — Loch Dochart, situated at the foot 
Ben More amid beautiful scenery, is the westernmost of the lochs 
belonging to the Tay branch of the Tay river-system, being evidently 
an expansion of the river Fillan, which forms the headwaters of this 
branch. It receives the drainage from a considerable tract of country, 
is very shallow, the bottom is very weedy, and there are many reeds, 
especially at the west end. Loch Dochart is nearly two-thirds of a 
mile in length, with a maximum breadth of nearly one-sixth of a mile, 
the mean breadth being over one-tenth of a mile, or 18 per cent, of the 
length. Its waters cover an area of about 46 acres, or nearly one- 
fourteenth of a square mile, and it drains an area of nearly 39 square 
miles, or 555 times the area of the loch. Nearly 70 soundings were 
taken in Loch Dochart, the maximum depth observed being 11 feet; 
but this depth is of very limited extent, only two isolated soundings 
being recorded near the west end of the loch, while by far the greater 
portion of the bottom is covered by less than 5 feet of water. The 
volume of water contained in the loch is estimated at 10,032,000 cubic 
feet, and the mean depth at 5 feet, or 46 per cent, of the maximum 
