168 On the Elevation of Beaches by Tides. 



will arise from the joint influence of both. Let us suppose, 

 that, from the abrasion of the channel, the latter tide arrives 

 each time one-hundredth of a second earlier than before. After 

 about 8150 years, the high water of the eai-lier tide will coin- 

 cide in point of time with the low water of the latter tide ; and 

 the difference of height between high and low water will be equal 

 to the difference of the height of the two tides, instead of to 

 their sum, as it was at the first epoch. 



If, in such circumstances, t!le two tides were nearly equal in 

 magnitude, it might happen that on a coast so circumstanced, 

 there would, at one time, be scarcely any perceptible tide ; and 

 yet, 3000 years after, the tide might rise thirty or forty feet, or 

 even higher; and this would happen without any change of relative 

 heightin the land and water during the intervening time. Possibly 

 this view of the effects which may arise, either from the wearing 

 down of channels, or the filling up of seas through which tides 

 pass, may be applied to explain some of the phenomena of raised 

 beaches, which are of frequent occurrence. 



Natural philosophers are at present not quite agreed upon 

 the mode of determining the mean level of the ocean. Whether 

 it is to be deduced from the averages between the highest and 

 lowest spring tide, or from the averages of all the intermediate 

 ones, or from the means of the instantaneous heights of the tide 

 at all intervening periods, or by whatever other process, its true 

 level is yet to be ascertained. It may, perhaps, be useful 

 to suggest that, besides the actual level of the sea at any parti- 

 cular place, it would be also desirable to ascertain whether the 

 time of high water at given epochs is not itself a changeable 

 quantity. These reflections, however, are only thrown out with 

 the view of exciting discussion on a subject involved at present 

 in great mathematical difficulties, and possessing, at the same 

 time, the highest practical importance.* — Babhagc's Bridge- 

 water Treatise. 



• The great temporary floods which have occasioned the deposition of the 

 remains of the ocean, considei ably above the level of the sea, such as the 

 great flood described by Boelhius, which, he says, " happened in the Ides of 

 October, in the year of Redemption 1097, carrying destruction into the coun- 

 try, overwhelming villages, castles, towns, and extensive woods/' may explain 

 some of these raised beaches. — Edit. I^i] 



