On the Power of Rainfall in Demidation. 225 



any change of the present order of things in the historical 

 period. Thus the ancient deltas at Menstrie, Alva, and Tilli- 

 coultry, figured and referred to by Mr Milne Home in his 

 " Estuary of the Firth of Forth," as ancient raised beaches, 

 may have been formed by some such sudden phenomena. Also 

 many of the upper sands and gravels (the series extends some 

 seventy feet deep in the Devon valley) may have been caused 

 by such sudden spates. The phenomena of the Devon and its 

 aftiuents are comparable to the mountain torrents on the 

 Italian rivers flowing from the Alps. 



These streams bring down great quantities of debris, but 

 do not cut out, but fill up. It cuts out the gravel and sand 

 below boulders before it carries them along, and heaps them 

 up as in the Dollar conglomerate bing. The largest stones 

 are carried the least distances, remaining at the summits of 

 the water-courses ; the gravels are carried farther out, but 

 sands mark the extremity of the torrential force. The stones 

 there are turned on their axes with great force and noise. 

 They thus acquire a centrifugal force, which causes them, to 

 leap on larger layers, and deposit themselves atop of them, as 

 at Dollar and Baldie's Burn. All this stops below the first 

 limits of the gravel. The force of the torrent, whetlier real or 

 effective, is proportionate to the square roots of the heights. 

 The rivers receiving those mountain torrents do not appear 

 to increase their contents by their sudden discharge into 

 them. This may be on account of their increased rapid flow. 

 The Devon Avas in no way apart from its ordinary quiet 

 aspect, either on the morning or throughout the day of the 

 floods. 



Wednesday, 20th February 1878.— Dr R. H. Traquaie, F.G.S., President, 

 in the Chair. 



The follo\\ing geutlemen were balloted for and elected as Resident Members : 



Professor Archibald Geikie, F.R.S., University of Edinburgh ; A. B. Brown, 

 Esq., 1 Rosebery Crescent; John Home, Esq., F.G.S., Geological Survey 

 Office, Victoria Street; John Christie Deans, Esq., M.A., S.S.C., 40 Castle 

 Street ; David John Surenne, Esq. , 6 Warriston Crescent ; Rev. John Macrae, 

 Parish Minister of Hawick, Roxburghshire; William Robertson, Esq., Actu- 

 ary, 55 Castle Street; and as Non- Resident, Norman Prentice, Esq., Civil 

 Engineer, Otago, New Zealand. 



