Mineralogy o/Sfy. 101 



period the strait of Kylehaken was narrower than it now is, the 

 same tide-wave which now passes through it would cause a much 

 -more considerable elevation of its tides. But it is already very 

 narrow, and no possible contraction that can be imagined would be 

 sufficient to produce a difference of elevation so great as would be 

 required for this purpose. It must be added to this difficulty that 

 the uniformly level surface of the plain is an insurmountable ob- 

 stacle to this supposition. 



In defect of any other solution it can only be supposed that thi» 

 is a fragment of some ancient diluvian deposit, instances of which, 

 although very rare in the islands, are sufficiently abundant upon 

 every part of the continent of Scotland. No estimate can be formed 

 of its original extent, nor can any valid conjecture be offered of the 

 mode in which it has been so abruptly cut down. It is however 

 likely that although the present direction of the tides is such as not 

 materially to exert any action on it, that direction may have varied 

 in the progress of time, from alterations in the shape of the bottom 

 of this very narrow channel, subjected four times in every day to the 

 alternating action of a most rapid stream, as well as from the probable 

 removal of a similar alluvium from the opposite shore of the main 

 land. As we find analogous causes producing daily and visible 

 changes of the same nature in the courses of rivers, the supposition 

 is not incompatible with facts, since the narrowness of the Kylehaken 

 channel and the rapidity of its tide, give it in this respect all the 

 characters of an inland river as far as the contraction extends. We 

 may perhaps indulge our conjectures still further in supposing that 

 Sky was once united to the main land by means of this alluvium, 

 and that the gradual effect of the tides circulating through the bay 

 on each side had at length produced the effect in question ; an effect 

 not at all inadequate to its powers, and of which parallel examples 



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