358 Dr. Mac Culloch on the Parallel Roads of Glen Roy. 



impression on the opposed angles at the point of flexure must be 

 different. Where the salient angle occurs it is plain that it will be 

 more subject to the effect of the water on the side which opposes 

 the current, than on that which declines from it. The same effect 

 will take place at the re-entering angle, but the corresponding sides 

 about the angle will be affected in the reverse order. If therefore 

 the current consists of a mixed mass of earth and water, the prin- 

 cipal deposit will be found to leeward of the salient angle, while 

 the windward side (if we may use this metaphorical term) will 

 remain clean. A similar effect, but in a reverse direction, will take 

 place on the re-entering angle, which however will be more marked 

 by the want of deposit on the side opposed to the stream, than 

 by any accumulation on the other side that includes the angle. 

 But if the current should have consisted of water alone, acting on a 

 previously deposited alluvium, the effects will be of a contrary 

 nature, since the greatest impression will, on both angles, be pro- 

 duced on the side that opposes the stream. Similar effects, but in 

 a more marked degree, must take place wherever such sinuosities 

 and furrows occur as to form a shelter to the sides from the direct 

 action of the current. Yet we have seen that the lines are traced 

 at the numerous indentations and flexures which Glen Roy ex- 

 hibits, with a total disregard of this circumstance, and with a degree 

 of equality that would have been impossible on such a supposition. 

 Another argument of a nature somewhat similar to this may be found 

 in the form of the upper part of Glen Roy, already fully described, and 

 to render it the more tangible, it is illustrated by a plan and section.* 

 Here the form of the ground produces a complete shelter from the 

 action of any current, which, like that supposed, must have been di- 



*P1. 18. PI. 21. Section M.N. 



