294 SKY. ALLUVIA. 



and of hornblende schist. It might perhaps be imagined 

 that the ordinary fragments of the mountains which back 

 this little plain, descending to the sea and there rolled, 

 might have been rejected by the tides so as to form these 

 banks ; but this supposition is invalidated partly by the 

 presence of gneiss and hornblende schist, which do not 

 occur among these mountains, and partly by the altitude 

 of the banks above the present high-water mark. It 

 must doubtless be granted that if at some more ancient 

 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 

 obstacle to this supposition. 



In defect of any other solution, it can only be supposed 

 that this 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 

 gf 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 rapid stream ; as well 

 as from the probable removal of a similar alluvium from 

 the opposite shore of the mainland. 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 the tide, give it 



