192 Miscellaneous — Caverns in the Chalk. 



Gloucestershire he formed a large collection of Liassic and Oolitic 

 fossils, among which were many remarkably fine examples of 

 Hippopodium 'ponderosum, Terebratula simplex, and T. plicata. 



We regret to record the death of Dr. H. C. Sorby, T.R.S., Past 

 President of the Geological Society, which occurred at his residence, 

 6, Beech Hill Road, Sheffield, on Monday, the 9th March, in his 

 82nd year. We shall write more fully of Mr. Sorby' s work in our 

 May jSTumber. 



DyCISOELIL..A.3SrE10"CrS. 



Natcral Caverns in Chalk. 



In a paper on the Chalk published in the Rochester Naturalist (see 

 vol. iii, 1907, pp. 466, etc.) Mr. S. Sills draws attention to the natural 

 chambers or caverns that have occasionally been encountered in well- 

 sinkings or borings in the Chalk. Thus Prestwich mentioned a cavern 

 that was proved in the Chalk at a depth of 270 feet below the 

 surface at Knockholt, near Sevenoaks. It was 30 feet long by 12 feet 

 wide and 18 feet high, with a stream of water running through it. 



Beneath the city waterworks at Strood, near Rochester, a natural 

 chamber was discovered in 1879. The cavern was found to be 

 roughlv Z-shaped on plan, the stem of the letter lying in the line 

 of a fault from north to south. The upper arm was 28 feet long and 

 10 feet wide, with a height of from 12 to 17^ feet; it appeared to 

 terminate in a tunnel-shaped fissure. The stem measured 16 feet 

 in length, Avith a width of 9 to \2^ feet. The lower arm was 

 18 feet long and from 3 to 10 feet in width, ending in a large fissure 

 which extended from floor to roof. 



Later excavations proved the fissure of the upper arm to be much 

 more extensive, and in 1903 it was explored to a distance of 130 feet 

 from the cavern, and was found to be 4 or 5 feet wide and 5 

 to 6 feet high. The floor was paved with a layer of tabular flint; 

 and the sides were scored, and in many places deeply undercut, by 

 the action of flowing water. The '- j-.!-'^ would appear to have found 

 its way primarily along the flint la- ■ ^lud, being intercepted by the 

 fault, was diverted to the big fissure wnere it found exit to the river. 

 The level of the flint layer is about one foot above low-water mark 

 of ordinary tides in the Medway, and the rise of the waters to 17 or 

 18 feet above this level would pen iip the stream until the ebb 

 released the waters. Fine sand and claj^ washed down, from strata 

 overlying the Chalk, through pipes and fissures, gradually silted up 

 the stream bed. The force of the stream being insufficient to remove 

 this silt, a fresh passage Avas carved out above it in chalk already 

 softened by the water's action. This process was repeated until the 

 present result was obtained. 



It was observed that at various points, where deviations in direction 

 took place, there were enlargements of the passage-like chambers ; 

 and that the excavation was both horizontal and vertical, while the 

 roof was drilled deeply, as if by a tool, in many places. 



