Geological Society of London. 113 



classify as traps. The dykes of basalt, howeYer, were not the only 

 modes of occurrence of this rock ; there were considerable flows of 

 basaltic lavas and occasional small craters. These volcanic districts 

 bear the name of Harra ; the principal are the Aneryid, the Khay- 

 bar, and the Kesshub. The last lies between Nejd Arabia and the 

 Mecca country. These masses of lava, etc., are comparatively modern ; 

 eruption, indeed, has in one or two localities occurred in historic 

 times, and steam has been seen to issue from certain craters. 



II.— February 6, 1884.— J. W. Hulke, Esq., F.K.S., President, 

 in the Chair. — The following communications were read : — 



1. " Delta in Miniature. — Twenty-seven Years' Work." By T. 

 Mellard Reade, Esq., F.G.S. 



' The author described a delta deposit, which, during a period of 

 twenty-seven years, had formed in the Eake reservoir (Rivington 

 Waterworks) from materials brought down by a stream of that 

 name. The reservoir at this part was divided by a road, water com- 

 munication being maintained by a culvert, once 8 feet high, now 

 almost silted up. The author described the stratification of these 

 deltas ; that near the influx of the Rake consisted of peaty matter, 

 gritty sand, gravel, shingle, and boulders of Millstone-grit up to 

 about one foot diameter. The other chiefly of fine sand with some 

 peaty matter. The former covered an area of 2508 yards, with an 

 average thickness of 2 yards ; the latter, an area of 430 yards, with 

 an average thickness of 3 yards. These materials had come from 

 the drainage-area of the Rake. This is estimated as 1"176 square 

 mile, and the delta being estimated at 6306 cubic yards, and the 

 time being 27 years, gives, as the annual rate of denudation over 

 the whole area, ^^2" incb per annum, or 1 foot in 5184 years. The 

 mean rainfall of the Rake Brook watershed for the last 10 years was 

 49-57 inches per annum. In this calculation no account is taken of 

 the finer materials which have doubtless been distributed over the 

 rest of the bed of the reservoir. The author pointed out that this 

 rate of denudation was rather more rapid than that of the Mississippi 

 (1 foot in 6000 years), and that the arrangement of the materials 

 imder the varying condition of the stream illustrated the phenomena 

 of lai'ger deltas. 



2. " On the Nature and Relations of the Jurassic Deposits which 

 underlie London." By Professor John W. Judd, F.R.S., Sec.G.S. 

 With an Introductory Note on a Deep Boring at Richmond, Surrey, 

 by Collett Homersham, Esq., A.M.Inst.C.E., F.G.S. 



The wants of the growing town of Richmond, in Surrey, have 

 necessitated the deepening of a well some years ago put down into 

 the Chalk, the water derived from which proves inadequate to the 

 present demand. The well has now been carried from a depth of 

 434 feet to one of 1310 feet. The work of boring has been per- 

 formed by Mather and Piatt's flat-rope machine, under the superin- 

 tendence of Mr. S, C. Homersham, C.E. Only insignificant quantities 

 of water have as yet been obtained ; but that this water is derived 

 from a deep-seated source is proved by the foUowiug facts : — it is 



