24 The Geology of Lochrutton. 



Marshy Flats. 



The Merkland Burn has contributed a much larger 

 amount of alluvium than its neig-hbour ; but considering the 

 relative size of the two streams, the Carswadda shows a 

 greater erosive power. This is explained by the rate of 

 wastage, varying in the different areas. The glacial deposits 

 lying across the head waters of the Carswadda are being- 

 rapidly removed and deposited in the Loch, but the Riggfoot 

 portion has been swept comparatively bare by ice-erosion. 

 Further, the Merkland Loch acted as a filtering pool, and^ 

 intercepting the suspensions, gave a pure feeder to the Loch. 

 When, however, the upper Loch was filled up the proportions 

 were reversed, and the largest feeder swept in huge quan- 

 tities of peat from its own store at an accelerated rate. 



The eastern shore contributes a larger quantity of waste 

 than the western ; consequently its sedimentation is greater, 

 especially near the mouth of the Minnin Burn. Had the rock 

 barrier at the Lade outlet been of a harder nature, and able 

 to keep the Loch at its original high level, the alluvial flats 

 would have been nearly horizontal from their highest point 

 inland. At the point where sedimentation ceased they would 

 have an abrupt slope towards the middle of the Loch. In 

 the case of a small stretch of water the sedimentation is 

 general and the deposit grows from the bottom upwards. 

 A rapid lowering of the barrier would have given us no 

 loch. As it is, there has been a fine balance of power. 

 Gradual erosion of the outlet has carried forward the point 

 .of sedimentation, and so produced a shelving slope at a 

 gentle angle of four or five degrees. 



The Barr Loch. 



In the Bogrie district the glacial drums lie along the 

 valley east and west, showing the direction of the Crocket- 

 ford ice. Near an pld shed there is a large boulder of 

 Arenig lava, which has its nearest outcrop in the Urr valley^ 

 many miles to the west. One of the drums lay in the path 

 of the newly-formed Lade, which was here augmented by the 

 Barr Burn from the west. This obstruction caused a block,. 



