66 



NATURE 



[May 17, 1900 



Loch Drunkie is a peculiar irregular little Highland lake, shut 

 in on all sides by high hills, situated, at an elevation of 416 feet 

 above sea-level, a quarter of a mile to the south of Loch Vcnna- 

 char, into which it flows. It is remarkable in shape, a quad- 

 rangular body throwing out three arms in different directions ; 

 the maximum length is over a mile, the maximum width of the 

 body over a quarter of a mile, and the area nearly a quarter of a 

 square mile. The greatest depth, 97 feet, was found near the 

 base of the north-eastern arm ; the mean depth is 36 feet. 

 Loch Drunkie was raised twenty-five feet in connection with the 

 Glasgow water-supply, for the purpose of supplying compen- 

 sation water to the River Teith. 



Lochs Voil and Doine formed at no distant date a continuous 

 loch, which has been divided into two portions by the material 

 deposited by the rivers. The level of these lochs being fifty feet 

 higher than that of Loch Katrine, it has been suggested that an 

 additional supply of water to Glasgow can be obtained by means 

 of a tunnel from Loch Doine to Loch Katrine through the 

 intervening hills. Loch Voil is over 3^ miles in length, about 

 one-third of a mile in maximum width, and covers an area of 

 nearly nine-tenths of a square mile. The greatest depth, 98 



IN 



I \ 



Temperature of LoCH KATRINE 



APRIL 1899 



JUNE 1897 



JUNE 1898 



-NOVEMBER 1897 



15 20 25 30 



35 10 45 50 55 60 65 70 75 8082/^ 

 FATHOMS 



Fig. 4. — Temperature of the water in Loch Katrine. 



feet, was found towards the western end ; the mean depth is 41 

 feet. Loch Doine is nearly a mile in length, and over a quarter 

 of a mile in maximum breadth, with an area of nearly a quarter 

 of a square mile. The greatest depth, 65 feet, was found 

 towards the eastern end ; the mean depth is 33 feet. 



Loch Lubnaig is one of the most interesting of the lochs 

 under consideration, the configuration of the bottom being much 

 more irregular than in any of the others. It receives the outflow 

 from Lochs Doine and Voil, its level being nine feet lower (405 

 feet above sea-level). The greatest depth, 146 feet, was found 

 approximately near the centre of the loch ; the mean depth is 

 42^ feet. The contour-lines of depth do not follow the contour 

 of the loch, hollows and ridges alternate with each other, and 

 in some places comparatively deep water is found close to the 

 shore, while in other places shallow water extends a consider- 

 able distance from shore. 



The deposits forming on the floor of these lochs are described 

 in detail, and the numerous temperature observations taken at 

 the surface and at various depths down to the bottom (some of 

 which were taken as recently as March 1900) are fully discussed. 

 The serial temperatures taken in Loch Katrine are shown 



graphically in Fig. 4. The relation between the variation of 

 temperature and the size and depth of the lochs is pointed out, 

 and shows how much more suitable a large deep lake is, as a 

 source of water-supply, than a shallow basin, ensuring a relatively 

 low temperature in summer and a relatively high temperature in 

 winter. Interesting observations were made on the pelagic and 

 other organisms in the various lochs, and on their variation with 

 the season, certain species being obtained in abundance at 

 certain seasons and absent or rare at other seasons. 



The amount of rain falling unnually on the drainage areas of 

 these lochs was estimated by three methods, the lochs being 

 grouped into two series, viz. Lochs Katrine, Achray, Drunkie 

 and Vennachar, which have their outlet at the eastern end of 

 Loch Vennachar. forming one series ; and Lochs Doine, Voil 

 and Lubnaig, which have their outlet at the southern end of 

 Loch Lubnaig, forming the other series. The readings of the 

 rain-gauges at all the observing stations within and near the 

 catchment-basins of these lochs were grouped together into two 

 series corresponding with the two series of lochs indicated, and 

 the average annual rainfall at the average height of the gauges 

 calculated for each series. By the first method, i\ per cent, of 

 annual rainfall was added for each 100 feet of mean height of the 

 catchment-basin above the average height of the rain-gauges, 

 and a figure thus obtained representing the average annual rain- 

 fall over the entire catchment-basin. By the second method, 

 the increase of 2\ per cent, per 100 feet of height was used to 

 calculate the probable annual rainfall at the same heights and 

 intervals as the contour-lines on the Ordnance Survey maps. 

 A third method was afforded by drawing lines of equal rainfall 

 on a map of the district. The total amount of rain falling on 

 the catchment-basins of the two series of lochs indicated was 

 calculated by these three methods, and the results obtained by 

 the first two methods agree very closely, while the results 

 obtained by the third method were in each case considerably 

 less The mean obtained by the three methods may probably 

 be regarded as a close approximation to the amount of rain 

 falling annually on these catchment-basins, viz. 14, 100 million 

 cubic feet for the Vennachar catchment, and 14,700 million 

 cubic feet for the Lubnaig catchment. 



~n the case of the Vennachar catchment a unique opportunity 

 is presented for comparing the outflow with the rainfall, for a 

 record has been taken twice a day of the depth of water flowing 

 over a weir at the east end of Loch Vennachar since Loch 

 Katrine has been made use of by the Glasgow Corporation as 

 the source of the water-supply to that city. 

 The readings ot the depth of the outflowing 

 water during the year 1869 have been calcu- 

 lated out, and the outflow for that year has 

 been estimated at 9572 million cubic feet. 

 The quantity of water supplied to Glasgow 

 during the year 1869 is estimated at 1660 

 million cubic feet. There is thus an excess 

 of rainfall, according to the mean of the 

 three methods, over the overflow of 2860 

 million cubic feet. This difference must be 

 accounted for by absorption, evaporation 

 and loss of water by underground channels. 

 The readings of the outflow for a series 

 of twenty-five years or more would be a 

 far more satisfactory basis for calculation than a single yejir's 

 readings (and the year 1869 was not an average, but a 

 very dry year), and it would be very interesting to have the 

 average annual outflow calculated over the whole period during 

 which the record has been kept, in the same way as the mean 

 annual rainfall is calculated for a particular station. Records of 

 the rainfall at high elevations in different parts of the catchrtient- 

 basins would also be desirable in comparing the average annual 

 rainfall with the average annual outflow. 



Appended to the paper is an account of the geology of the 

 district by Messrs. B. N. Peach, F.R.S., and J. Home, F.R.S., 

 based on materials collected during the Geological Survey of 

 that region, and published by permission of Sir Archibald Geikie, 

 the Director-General. A brief sketch is given of the ge ological 

 structure of the area embracing the various lochs, which has an 

 important bearing on the question of the evolution of the valley- 

 system. It is shown that, along the Highland border, there is a 

 great development of conglomerates, grits and greywackes, be- 

 longing partly to the crystalline schists and partly to the Old Red 

 Sandstone. These strata, being vertical or nearly so, would be 

 much less easily eroded than the gently inclined schistose rocks 



NO. 



1594, VOL. 62] 



