344 Prof. Rogers on the Origin of the Parallel Roads. [March 22, 



accumulated by currents or glaciers from Ben Kevis, can be regarded as 

 admissible, inasmuch as there are no traces of any such in any of those 

 localities where alone we can assume them to have existed to produce 

 the required embaying of the waters. In this entire absence of all 

 remnants of the supposed natural dams across the glens, it is most 

 unphilosophical to take for granted their total obliteration, where no 

 cause has or can be assigned which can have so effaced them. 



On the other hand the hypothesis of successive " sea margins," or 

 sea levels, is overthrown by the now well-established deduction from 

 the speaker's own recent measurements, that none of the several shelves, 

 or " roads," of Glen Roy correspond in level with any of those seen 

 in the adjacent valley Glen Gluoi, a marked discrepancy separating 

 the two groups of terraces into two independently produced systems. 

 It can be shown, moreover, that these discordances of interval between 

 the shelves of the glens respectively, are such as cannot be accounted 

 for on any supposition of " faults," or dislocations of the earth's crust, 

 in the ground between the two glens. Equally incompatible are all 

 the facts of the relative levels of the shelves, with the notion that they 

 are possibly sea beaches which may have undergone an unequal amount 

 of elevation by an oblique secular rise of the land, such as is known to 

 be very gradually taking place on some coasts at the present day. The 

 individual terraces are too nearly level to admit of this explanation ; 

 since so wide a warping of the crust from horizontality within so limited 

 a space as separates the two glens, would have left them conspicuously 

 sloping. Besides, the two systems of shelves are wholly insulated from 

 each other, and the notion of their origin as sea beaches gradually 

 elevated implies a continuity between them, together with certain 

 agreements in their directions of derivation from levelness which we 

 wholly fail to perceive. 



In conclusion, the speaker proceeded to sketch the action to which 

 he ascribes the formation of all these shelves or parallel roads. He 

 supposes the several terraces to have been cut or grooved in the sides 

 of the hills by a great inundation from the Atlantic, engendered by 

 some wide earthquake disturbance of the ocean's bed, and forced 

 against the western slope of Scotland. The features of the country 

 indicate that, while a portion of such a vast sea-tide entering the Firth 

 of Linnhe rushed straight across the island through the deep natural 

 trench, Glen Mor, or the great Caledonian valley, a branch current 

 was deflected from this, and turned by the Spean valley and its tribu- 

 tary glens, Glen Roy and Glen Gluoi, into the valley of the Spey, 

 and so across to the German Ocean. In this transit, the deflected 

 waters first embayed in these glens, and then filling and pouring 

 through them, would, upon rising to the levels of the successive water- 

 sheds, or low passes, which open a way to the eastern slope of the island, 

 take on a swift current through each notch, and as long as the outpour 

 nearly balanced the influx, this current, temporarily stationary in 

 height, would carve or groove the soft " drift " of the hill-side. But 

 the influx increasing, the stationary level and grooving power of the 



