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 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
