TEANSACTIONS OF SECTION C. 7il 



mite floor, from six to twelve inches tliick, formed on a reddish cave-earth having a 

 maximum thickness of fourteen inches, and lying on a continuous limestone basis. 

 Beyond a few remains of hysena nothing of interest occurred in the stalagmite, hut 

 the contents of the cave-earth were more numerous and interesting. In July 1887, 

 twenty-four specimens of bones selected from Mr. Else's finds — twenty-one being 

 from the cave-earth in tlie tunnel and three from the dyke — were forwarded for identi- 

 fication to Mr. E.T.Newton, of the Geological Survey of England, who at the end of a 

 very few days returned them with a list containing not only the names of the species 

 to which they belong, but also those of the bones themselves. Of the twenty-one from 

 the tunnel one is a relic of fox, while all the others are those of the cave-hyaena. 

 The three from the dyke represent the cave-hear, Rhinoceros tichorhinus, and a species 

 of deer. Among the tunnel finds there were also three coprolites and a solitary part 

 of a left lower jaw of hycena divested of its lower border — two facts indicating 

 that the hyaena occasionally visited the tunnel. Here also was found one, and but 

 one, flint-tiake tool. It has the white colour so prevalent in the tools found in 

 the cave-earth of Kent's Hole, and was met with under circumstances admitting 

 apparently of no doubt of its having been made and used by a human contemporary 

 of the cave-hyfena in Devonshire. 



2. The Natural History of Lavas, as illustrated hy the Materials ejected 

 from Krakatoa. By Professor J. W. Judd, F.B.S., Pres.G.S. 



As a member of the Krakatoa Committee of the Royal Society, the author had 

 been called upon to study the various substances ejected from Krakatoa during the 

 great eruption of 1883. All the lavas which have issued from the central vent of 

 that volcano, since its first formation, belong to the class of the enstatite-andesites. 

 The chemical and mineralogical characters of these rocks have been very fully in- 

 vestigated by Richard, Renard, Sauer, Oebekke, Vom Rath, Reusch, Winkler, 

 Waller, Carvill Lewis, Joly, Breon, and especially by Verbeek and Retgers ; and 

 the further study of these rocks in the light of these researches suggests some 

 conclusions of great geological interest. 



A comparison of these enstatite-andesites with others which have been studied 

 with similar care, such as the rocks of Santorin, of the Bufi'alo Peak, Colorado, 

 and of the Cheviot Hills, reveals some very striking facts. In all of these rocks the 

 minerals present are the same — namely, various species of plagioclase felspar, a 

 ferriferous enstatite, an angite and magnetite with ilmenite ; these minerals being 

 embedded in a more or less perfectly glassy base which has nearly the same com- 

 position in all of them. Yet some of these rocks on analysis are found to be basic 

 in composition, containing only 51 per cent, of sUica, while most of them are 

 intermediate, and some, the rocks of Krakatoa for example, are distinctly acid, 

 having over 70 per cent, of silica. The cause of these differences is found in the 

 fact that the quantitative mineralogical constitution is so varied. Some have 

 only 10 per cent, of glass and 90 per cent, of porphyritic crystals, while others 

 have 90 per cent, of glass and only 10 per cent, of crystals. 



Although the enstatite-andesites of Krakatoa are all identical in chemical 

 composition and in mineralogical constitution, they nevertheless present us with 

 three very distinct types of rock. Among the older masses we have a stony lava 

 which graduates into a black porphyritic pitchstone. Among the later ejections 

 we find a porphyritic obsidian, which on being distended by the escape of gas 

 forms the well-known Krakatoa-pumice. While the stony lava and pitchstone 

 have a very high fusion-point, the obsidian, which contains a considerable quantity 

 of water, melts at a comparatively low temperature, and in doing so swells up to 

 five or six times its original bulk, forming a true pumice. 



The bearing of these facts upon some important geological problems is con- 

 sidered, and reasons are given for doubting whether the porphyritic crystals in a 

 lava have necessarily been developed in the masses in which they are now found. 



The important considerations suggested by the late Dr. Guthrie, as the result 

 of his study of the ' cryohydrates ' and ' entectic-alloys ' are dwelt upon, and it is 

 shown that the silicates, like other salts, have their fiision-points lowered by 



