Geological Society. 65 



flection of the river, as a straighter course appears open to it by 

 White Waltham to Bray : this line was surveyed for a canal by 

 Mr. Brindley, and appears to be level to White Waltham, and thence 

 to fall 47 feet to Mankey island, near Bray; so that a dam of a fewr 

 feet across the river below Sunning at the mouth of the Loddon, 

 would turn the waters into this channel. The author conceives the 

 most natural mode of explaining this deflection of the river, is by 

 the supposition that a higher range of tertiary strata once extended 

 from the ridges of Bagshot-heath in this direction ; forming a bar to 

 the progress of the stream in this line. 



V. The plains of London are covered with enormous accumulations 

 of water-worn debris, chiefly of chalk-flints, and often abounding in 

 fossil remains of elephants, hippopotami, &c. ; the gravel is not 

 confined to the low grounds, but caps the highest summits of the 

 district; e. g. Highgate on the north, and Shooter's Hill on the south 

 of the river. To explain this distribution of this gravel by the ope- 

 ration of the actual rivers, the author observes that it is necessary, 

 first, to suppose that an uniform plane originally existed from the 

 summit of Highgate to the Hertfordshire chalk downs, and from the 

 top of Shooter's Hill to those of Kent ; on the surface of which the 

 rivers once flowed. 2ndly, That these rivers have subsequently washed 

 away all that immense mass of materials which would be requisite 

 thus to reconstruct the surface ; and 3rdly, That having worn down 

 that surface into nearly its present form, the rivers perpetually shifted 

 their channels so as to distribute the gravel equally over the whole 

 plain of London, yet remained long enough in each channel to 

 lodge there deposits of this gravel 20 or 30 feet thick. 



A paper was also read entitled, " A few facts and observations as to 

 the power which running water exerts in removing heavy bodies," by 

 Matthew Culley, Esq., F.G.S., &c., in a letter to Roderick Impey 

 Murchison, Esq., Sec. G.S., F.R.S., &c. 



The heavy rains which fell during three days of August, 1827, 

 swelled to an unusual height the small rivulet called the College, 

 which flows at a moderate declivity from tlie eastern watershed of 

 the Cheviot hills, and caused that stream not only to transport 

 enormous accumulations of several thousand tons weight of gravel 

 and sand to the plain of the Till, but also to carry away a bridge then 

 in progress of building, some of the arch-stones of which, weighing 

 from 5 to f of a ton each, were propelled two miles down the rivulet. 



On the same occasion, the current tore away from the abutment of 

 a mill-dam a large block of greenstone-porphyry, weighing nearly 

 two tons, and transported the same to the distance of a quarter of a 

 mile. Instances are related to occur repeatedly, in wiiich from one 

 to three thousand tons of gravel are in like manner removed to 

 great distances in one day ; and the author asserts, that whenever 

 400 or iiOO cart-loads of this gravel are taken away for the repair of 

 roads, that one moderate flood replaces the amount of loss with the 

 Name (|uuntity of rounded debris. 



Parallel rases of the power of water are stated to occur in the 

 Twet'd, near (,'oldslreum. 



.V.N. VoI.G. No. .'ii. J?//j/ 1829. K ASTKO- 



