Narrow Fissures Research Articles

Recent researches in Bench Cavern, Brixham, Devon

About the end of March 1861, nearly two years after I had completed the exploration of the famous Brixham Cavern, more correctly known as ‶Windmill Hill Cavern, Brixham,″ information was brought to me that ‶another bone cave″ had just been discovered very near that town. I at once proceeded thither, and ascertained that the new ‶find″ was in the northern or Torbay slope of Furzeham Hill, between which and Windmill Hill the town of Lower Brixham mainly stands. Considerable limestone quarries have from time to time been worked in this slope, and one of them, known as Bench Quarry, had been all but abandoned as long ago as 1839; but quarrying had been resumed there in 1861, and had led to the discovery about which I had gone to inquire. The workmen had laid bare a vertical wall-like mass or dyke, composed of red earth, angular pieces of limestone, and bones, all cemented firmly together and to the back wall of the quarry. The base of the dyke was 96 feet above spring-tide low water, and its summit 123 feet above the same level. The dyke itself was 27 feet high, 12 feet long, and from 2 feet to 3 inches thick. It was obvious that the materials composing it had from time to time fallen into a narrow fissure in the limestone hill. Mr Wolston, the proprietor, informed me that, as early as 1839, the whole of the outer surface of the dyke was laid bare, with the exception

V.—Note on the occurrence of Scorodite, Pharmacosiderite and Olivenite in Greenstone at Terras Mine, St. Stephens

At Terras mine there is an interesting junction of a well-marked tin-bearing elvan, whose course is about north and south, with a bed of greenstone, whose general bearing is nearly east and west. Near the junction, a few years since, a shaft was sunk 40 fathoms deep for the purpose of working a tin lode which was believed to cross the elvan just refered to at that point. At a depth of about 10 fathoms the bed of greenstone was met with, and it continued for 6 fathoms in depth in a very hard state, but from thence to the bottom of shaft it was much softer.The rock is one of the hardest and toughest I have ever come across. Ordinarily it is composed of a fine-grained mixture of hornblende and silica, but it contains numerous narrow cavities or partial fissures, which near the shaft in question are often studded over or lined with small crystals of the three arseniates mentioned above.

II.—On the Supposed Influx of Water to the interior of the Globe, as the Cause of Volcanic Eruptions

It is now generally recognised that the power which forces up lava from a depth of miles through narrow and crooked fissures broken across the solid crust of the globe, is no other than steam, developed in the interior of the lava by vaporisation of water intimately disseminated throughout its substance. I am not aware that previously to the publication of my volume on Volcanos in 1825. But I had derived a conviction of 1822, and a study of Etna and Stromboli in the years 1819–21. This was subsequently confirmed by the discoveries of Sorby, Scheerer, and others, of the existence of water in intimate molecular combination with the crystalline or granular minerals that compose the granitic rocks from the fusion of which lava is supposed to proceed. I had expressed my belief that the aqueous particles so confined, whether in a liquid or a solid state, would upon the occurence of increased heat, or diminished pressure, exert an elastic separating force upon the solid crystals of granules, in the manner of a flux, and thus assist the liquefaction of the mass, and drive it up any fissure that might open for its passage, in a pasty or semi-liquid state, short of complete fusion; so that on reaching the outer air, and parting with the contained steam, together with the heat which the expansion of this element would carry off in a latent from, its surface would consolidate instantly; and the solidification extending rapidly inwards by the formation of crevices giving an outlet to further vapour, the resulting rock would exhibit a cellular or porous structure, and a granular or crystalline texture, in lieu of the compact and glassy one which, if completely fused, it should possess.