14 The Geology of Lochrutton. 



sequently these paiallel ridges with their intervening hollows 

 follow the same direction. When it is remembered that all 

 the older streams and principal lochs have also an east and 

 west trend, then we will at once see the powerful effect that 

 the arrangement of the strata and its subsequent weathering 

 ha\e had upon the original drainage system of the area. 



The Glen Burn gives an excellent illustration of the 

 way in which a running stream pierces the rocks and shales. 

 The course of the stream differs by a few degrees from the 

 direction of the strike. The burn has excavated the shales 

 for a few yards, and then crossed the hard greywacke at 

 right angles until it encounters the next strike of shales. 

 Ihe result is an east and west drainage with occasional 

 zig-zags. 



The form of the surface has since been greatly modified 

 by the powerful effect of glaciers during- the Ice Age. In 

 some places the old land surface has been wholly changed. 

 Great quantities of decayed rock rubbish have been removed, 

 laying bare the unweathered surface. In other districts 

 the retreating glaciers have deposited large accumu- 

 lations of glacial drift. These deposits of the Glacial Age 

 are distributed throughout the district in an interesting- 

 manner, and have a strange diversity of form and height, 

 according to the conditions and size of the glaciers. ~ 



A general survey of the Loch will show at a glance 

 that its formation is geologically of very recent date, and 

 also that any change since effected, either in the way of 

 accumulation or removal, is clearly defined and can be easily 

 measured. 



Before dealing with the method of loch formation and its 

 subsequent history of change, we must consider carefully 

 the physiographical conditions that existed on that spot 

 immediately before the Loch was formed. It is only by 

 such means that a true estimate can be formed of the 

 original contour of the lake floor and the amount of altera- 

 tion since effected. 



Age. 



Both the lake and the alluvial flats which originally 



