THE FRESH- WATER LOCHS OF SCOTLAND. 39 



allowance to be made for absorption by vegetation and for loss by 

 evaporation, and he calculated that the average annual amount of water 

 absorbed and evaporated is equal to about 13 inches of rainfall. On 

 this basis, and assuming for the present that the evaporation from the 

 surface of the water is equal to absorption and evaporation from the 

 land, the total amount of water lost through absorption and evaporation 

 over the entire catchment-basin of Loch Vennachar would be about 

 2,273,885,000 cubic feet per annum.* Comparing this figure with the 

 figures given above showing the excess of rainfall over outflow, we 

 observe that, according to the mean of the three methods, the difference 

 between the rainfall and outflow is greater than would be accounted for 

 by absorption and evaporation as estimated by Leslie, there being an 

 excess according to the first two methods, and a deficiency according to 

 the third method. 



The foregoing figures, calculated for the year 1869, show that the 

 rainfall unaccounted for by outflow at Coilantogle, and supply of water 

 to Glasgow, is according to the first method 26 per cent., according to 

 the second method 27 per cent., and according to the third method 

 8 per cent. : this percentage must be referred to loss by absorption, 

 evaporation, and the loss of water through underground channels. 



NOTES ON THE GEOLOGY OF THE LOCH KATRINE DISTRICT. 



By Messrs. BEN. N. PEACH, F.R.S., and JOHN HORNE, F.G.S., from 

 unpublished observations made during the course of the Geological 

 Survey of Scotland. With Geological Map (Plate II.). Published 

 by permission of Sir Archibald Geikie, D.C.L., F.R.S., Director- 

 General of the Geological Survey of the United Kingdom. 



The lochs in this district to be first treated of, with the exception of 

 Loch Arklet, lie within the catchment-basin of the river Teith above 

 Callander. Though situated about a mile to the west of Loch Katrine, 

 the small lake, Loch Arklet, drains into Loch Lomond. 



1. Geological Structure of the area embracing these Lochs. 



All the lochs, save the lower part of Loch Vennachar, lie within the 

 territory of the crystalline schists of the Highlands, which are bounded 

 along the Highland border by a powerful fault stretching from Stone- 

 haven to the Firth of Clyde. As shown on the geological sketch-map, 

 this dislocation extends from Aberfoil north-east by Leny to Luirgeann 

 on the Kelty water. On the south-east side of this fault the strata 



* The evaporation from the surface of the lakes will, of course, exceed Leslie's figures 

 for loss through absorption and evaporation. 



