1 861.] of the Parallel Roads ofLochaher (Glen Boy), Scotland. 343 



or valley adjoining, a coincidence suggestive of the notion that they 

 were formed by the grooving agency of a flood pouring through the 

 glens while it was embayed at the respective levels of these natural 

 waste weirs. In confirmation of this view that they were transiently 

 caused by erosive currents held successively at the heights of the bar- 

 riers on whose levels the terraces terminate, we have as another in- 

 teresting general feature, a remarkable ruggedness of the bed of each 

 external glen just outside the water-shed or barrier closing the glen 

 which contains the terrace. These rough and deep ravines, contrasting 

 strikingly with the smooth spoon-like terminations of the terrace-lined 

 glens which head against them, strengthen the suggestion already 

 awakened by the marks of horizontal erosion in the terraces themselves, 

 that the notches or passes which determined the grooving of the hill 

 sides on their one hand were externally the sites of so many stupendous 

 cataracts. 



The internal structure or disposition of the matter composing each 

 terrace, affords a further and striking corroboration of this hypothesis 

 of the passage of an erosive flood. It consists in an " oblique lamina- 

 tion," or slant bedding of the constituents of the shelves ; viz. the 

 layers of gravel, sand, and other sediment, such as geologists familiarly 

 recognize as the result of a strong current pushing forward the frag- 

 mentary material which it is depositing, and which is held by them to 

 indicate in the direction towards which the laminae dip, the direction 

 towards which the current has moved. Now it is a most suggestive 

 peculiarity in the oblique bedding of these terraces, that the " dip," or 

 downward slant, is almost invariably up the glen, or towards its head, and 

 not dawn the glen, or towards the Atlantic, as we must suppose it would 

 have been, had the glen been a bay of the sea, and these materials but 

 portions of ordinary sea beaches. Indeed, this feature is of itself enough 

 to suggest an origin due to a strong current sweeping inward from the 

 Atlantic, and across the water-shed of the island to the opposite sea. 



The speaker next proceeded to examine the hypotheses of his pre- 

 decessors in this inquiry respecting the origin of the Parallel Roads. 

 They all assume the agency, in one form or another, of standing water, 

 either the ocean in its ordinary state of repose, or lakes pent within the 

 glens. 



The notion that a quietly resting sea has fashioned these level shelves 

 is refuted by the fact, that they are not true marine beaches ; they ex- 

 hibit none of the distinctive features of genuine sea-shores, not a vestige 

 of any marine organic remains, no rippled sands, no shingle, and no sea 

 cliffs. They display in like manner a total absence of the distinctive 

 marks of lake sides ; not one lacustrine organism, neither fresh-water 

 plant, nor animal having ever been discovered imbedded in them. A 

 further difficulty attends the lake-hypothesis in the necessity it imposes 

 of discovering a feasible cause of blockage of the glens at different 

 stations above their mouths, to pond the waters to the respective heights 

 of the terraces. Though much ingenuity has been expended upon this 

 part of the problem, no suggestions yet offered of barriers of gravel, 



