THE FRESH-WATER LOCHS OF SCOTLAND. 329 



lip of the basin, above the point where the loch discharges into the 

 river Hope, is composed of Lewisian gneiss on the east side and 

 Cambrian quartzites on the west. No rock is visible at the mouth of 

 the lake, nor in the course of the stream that connects it with the sea. 

 On either side of the river Hope there are alluvial terraces, eroded 

 partly out of solid rock and partly out of raised beach deposits. There 

 are the remains of the 100-feet beach by the river Hope, and of the 

 50-feet beach at the head of the lake ; hence it is evident that during 

 their deposition the sea must have extended far up the valley. 



The lower portion of the lake lies along a line of fault trending 

 nearly north and south, which is evidently continued northwards along 

 the channel of the river Hope, though concealed by the alluvial deposits. 

 On either side of this line there has been a lateral shift of the outcrops 

 of the various groups of rock, indicating a downthrow to the east. This 

 dislocation has been proved to traverse that portion of land that juts 

 into the loch on the west side about a mile south of Poll Ath-roinn, 

 where the quartzose flagstones of the Moiiie series have been thrown 

 down against a narrow belt of deformed Lewisian gneiss. Though the 

 whole of Strath Mor (the valley above Loch Hope) has not been mapped 

 by the Geological Survey, it is not improbable, judging from the straight 

 feature, that the fault may be prolonged southwards, and may have 

 been a prominent factor in determining the original course of the valley. 



Though no rock is seen at the outlet of the lake, it is not improbable 

 that it may be a rock basin. Its widest and deepest part lies within 

 the area occupied by the eastern or Moine schists (Geological Survey), 

 just above the belts of displaced and deformed Lewisian gneisses and 

 the crushed schistose rocks in association with them. Bounded by the 

 75-feet contour-line, this upper basin extends for 1| miles above the 

 narrows, with an average breadth of one-third of a mile. A second 

 basin, with a maximum depth of 104 feet, occurs further down, opposite 

 Poll Ath-roinn, which is carved out of a belt of Lewisian gneiss and 

 the mylonized rocks above the Moine thrust-plane. 



As the surface of the water in Loch Hope is only 12 feet above sea- 

 level, the greater part of the lake is below the level of the sea. 



The striae and the distribution of the drift indicate that during the 

 early and later glaciatioiis the ice moved from the south towards the 

 north, so that the trend of the lake coincides generally with the 

 direction of ice-movement. 



Loch Laoghal, Loch Creagach, and Loch Slaim. The rocks under- 

 lying this chain of lochs consist of hornblendic gneisses exposed on 

 either side of Loch Slaim, of granulitic micaceous gneisses of the Moine 

 series, and the granite of Beinn Laoghal and Beinn's Tomaine. Along 

 the northern margin of this granite mass the strike of the schists is 

 nearly east and west, the general dip of the foliation planes being 

 towards the south at angles varying from 20 to 70. These rocks are 



