74 BATH Y METRICAL 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 7 5 -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 0> 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 1 1 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 



