TRANSACTIONS OF SECTION C. 665 



tidal estuaries. These banks, instead of presenting sloping planes or concave 

 surfaces, are always convex when the matter of which they are formed is soft and 

 yielding. A section of such a pair of banks would present an approximation to a 

 cusp in the middle portion. 



This peculiar outline is manifest!}' due to the action of water on the yielding 

 matter. A few years since I found a result which may assist in exploring this- 

 phenomenon. The velocity of water in a channel is well known to depend on the 

 ratio of the area of the cross-section to its perimeter. This ratio is variable in all 

 known channels of water flowing through rigid materials such as canals and rivers. 



On investigating the form of section corresponding to a constant ratio of the 

 quantities referred to, I found that it would be represented by a pair of catenaries 

 with their ends meeting so as to form a cusp like that in the estuary channels.^ 

 The result would be that, with every depth of water in such a channel, the flow 

 would have nearly the same velocity. 



7. Report of the Committee on Earth Tremors. — See Reports, p, 145, 



8. Interim Report of the Committee on the Investigation of a Coral Reef 



9. Report of the Committee on Underground Waters. — See Reports, p. 283. 



1 0. Report of the Committee on the Marine Zoology of the Irish Sea. 



See Reports, p. 318. 



11. On a Keuper Sandstone cemented by Barium Sidphate from the 

 Peakstones Rock, Alton, Staffordshire. By W. W. "Watts, M.A., F.G.S, 



Professor F. Clowes ^ has described a sandstone from the Himlack Stone, near 

 Nottingham, in which the grains are cemented with crystalline barytes, the 

 amount of this material varying from 28 to 50 per cent, in ditt'erent specimens. 

 This rock occurs at the base of the Keuper Sandstone of that locality. A some- 

 what similar rock, occurring at about the same horizon, is described by Mr. A. 

 Strahan,'' from Beeston Castle in Cheshire, and the same author refers to the frequent 

 occurrence of barytes in the Keuper breccias. 



Bearing these facts in mind, the writer visited a curious isolated stack of rock^ 

 called the ' Peakstones Rock,' near the village of Alton in Staflbrdshire, which is^ 

 figured in Professor Hull's memoir on ' The Triassic and Permian Kocks of the 

 Midland Counties of England.' This stack is made of the lower beds of Keuper 

 Sandstone, but its outer portion has lost whatever cement it may once have con- 

 tained. It is, however, situated at the end of a spur which projects into a valley,, 

 and exposes a good deal of bare rock. This rock contains what at first look like 

 several veins of barytes two or three inches thick, striking along the spur and 

 straight through the place occupied by the Peakstones Hock. On examination of 



' Proceedings of the Jloyal S:iciety, vol. xliv. p. 108. 



2 Rep. Brit. Assoc, 1885, p. 1038 ; 188i), p. 694 ; 1893, p. 732 ; and Proc. Roij. 

 Soc, vol. slvi. pp. 363-369. 



' Mem. Geol. Survey. Exp. Quarter Sheet, 80, S.W., p. 7. 



