THE FRESH-WATER LOCHS OF SCOTLAND. 49 



enclosed by the 90-feet contour-line, and the deepest sounding being 

 97 feet. A fault, with a downthrow to the west, crosses the head of 

 the loch at the Trossachs Hotel, which has produced considerable 

 brecciatioii of the strata, a feature probably continued along the floor 

 of the loch between the hotel and Achray. The greater part of this 

 lake is on the upthrow side of the fault just referred to, and the basin, 

 as already indicated, has been excavated mainly in slates. 



Loch Vennacliar. Between Loch Achray and Loch Vennachar there 

 is a strip of alluvium, the difference in level between the two lakes 

 being 6 feet. The successive terraces show that these two lakes 

 originally formed one sheet of water, which stood at a somewhat 

 higher level. Loch Vennachar contains one prominent basin, about 

 2 miles in length, enclosed by the 50-feet contour-line. Within this 

 limit there are two smaller basins, which fall below the level of the 

 100-feet contour-line (see Plate V.). The deepest sounding is 111 feet, 

 which occurs to the north-east of Invertrossachs, on the line of the great 

 boundary fault along the Highland border, which has a downthrow 

 to the south-east. West of this dislocation the floor of the lake rises 

 sharply to a level of 20 feet below the surface. Westwards, however, 

 near Lanrick, the depth increases to 50 feet, a feature which coincides 

 with the course of two faults crossing the loch branches of the Loch 

 Tay fault, ancl each having a similar downthrow to the west. Doubtless 

 where the deep soundings coincide with lines of fault, the strata have 

 been much shattered and crushed, which has led to the more rapid 

 disintegration of the materials. But though these faults may have led 

 to local modifications of the floor of the lake, they obviously do not 

 account for the excavation of the basin. The long, narrow hollow, 

 crossing obliquely these lines of dislocation, points to glacial erosion. 



Loch Drunkie. Reference has already been made to the geological 

 features of this basin (see p. 42). In the western portion of the west 

 branch, where the hollow has been scooped out of slates, a small part 

 of the floor is enclosed within the 50-feet contour-line. The deepest 

 sounding, 97 feet, occurs in the north branch of the lake in front of a 

 ridge to the east, which rises to a height of about 150 feet above the 

 loch. The direction of the striae at Loch Drunkie is E. 20 S., and 

 the deepest sounding is found where the erosion must have been 

 greatest. 



Loch Arklet. This lake lies across the path of the great ice-sheet, 

 and coincides with the trend of the later movement (see pp. 44 and 

 45). Both the north and south shores of this loch are surrounded by 

 moraines, but though such is the case the stream flows over solid rock, 

 where it leaves the alluvial flat 1J miles west of the outlet, and con- 

 tinues to flow for half a mile over solid rock. Originally the lake must 

 have extended westwards to this barrier, for the intervening strip cf 

 alluvium has been laid down by the burns joining the Arklet water not 



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