:W Remarks on the Fonaation ()/' Alluvial Deposites. 



By a singular coincidence, these two gentlemen introduced 

 the subject to the notice of men of science nearly at the same 

 time, and each gave a separate account of the process, by which 

 he supposed the terraces to be produced. Both conceived them 

 to be formed by the action of waves, impelled by wind against 

 the shores of an ancient lake; but Sir T. Lauder (1. c. p. 15.) 

 supposed the waves to form the terrace, by eroding the banks 

 alono-the edge of the water ; and Dr ?.Iacculloch (1. c. p. 371 ), 

 by thiowing back the pebbles as (m a sea-beach. 



To Sir T. Lauder's explanation it may be sufficient to reply, 

 that such erosion of the banks utterly exceeds the power of 

 simple water, and that the banks above the margin of the lakes 

 do not exhibit the concavities, which would denote the erosive 

 action of waves, but descend into the water with the same forms 

 and appearances which are to be seen on mountain-sides in or- 

 dinary circumstances. 



To Dr MaccuUoch's explanation it may be objected, 

 1*^, That many of the stones which lie upon the terraces, are 

 from one to four feet in length, and that the waves could never 

 have moved them. 



^dly, That the stones of which these terraces consist are 

 commonly angular, and as sharp as those on the mountain-side 

 above the terrace, and that rolled pebbles are only found where 

 brooks and torrents enter the lake over beds, likewise consisting 

 of rounded stones, which have been transported from a distance, 

 and so shaped in their passage. 



3%, That banks or terraces, thrown up by waves, are only 

 found on gently sloping beaches, and then ouly where the mo- 

 tion of the pebbles is not impeded by their being enveloped in 

 clay. 



Stilly, That in the case of a terrace formed by the action of 

 waves, the edge of the water coincides with the top of the steep 

 declivity, so that, according to this explanation, the surftice of 

 the lake ought to reach only to the point c (Fig. 23.), instead 

 of rising above the slope from c to h, as it uniformly does. 



There are undoubtedly cases, where the waves form terraces 

 on the borders of lakes as well as of the ocean. I saw an instance 

 of this on the shelving beach at Neuchatel, and remarked, that 

 the sound of the pebbles and the other appearances were the 



