506 . G. M. Davies — CJiromite in Beer Stone, 



Probably an acquaintance with modern active volcanoes would lead 

 one to attribute the phenomenon solely to a breaching of the cone on 

 its northern side by later explosions. Such speculation, however, 

 does not appear quite witbout interest, especially where other 

 evidences are so little available. 



For the photographs which illustrate this paper it is a pleasure to 

 express indebtedness to Mr. John C. Caldwell, M.A., of the Madras 

 College, St. Andrews. 



EXPLANATION OP PLATE XIII. 

 Fig. 1. — Eock and Spindle shore stack, 2 miles east from St. Andrews. The 

 fossilfish-teeth reported on by Dr. Smith Woodward were collected 

 from the centre of the Spindle. 

 ,, 2. — Concentric arrangement of ash layers, Eock and Spindle. In the 

 distance may be seen the stratified rocks beyond the eastern margin 

 of the vent. 



III. — Chromitk in Beer Stone. 

 By G. M. Davies, M.Sc, F.G.S. 



THE Beer Stone is a gritty limestone, made up largely of shell 

 fragments with some foraminifera, quartz grains, and soft 

 chalky material, occurring in the Rhynchonella Cuvieri zone of the 

 Middle Chalk near Beer Head in the south-east of Devon. It has 

 long been worked for building purposes in underground galleries 

 about one mile west of the village of Beer, and has been described 

 by W. Hill and "W. F. Hume in the Geological Survey memoir on 

 the Lower and Middle Chalk. 1 Dr. Hume records the following 

 minerals as present in the insoluble residue of the stone: quartz, 

 muscovite, glauconite, chalcedony, pyrites, tourmaline, rutile, 

 andalusite, and possibly anatase. 2 A. J. Jukes-Browne 3 says the 

 residue " contains a variety of minerals which have clearly been 

 derived from land consisting of granite and Palaeozoic rocks such 

 as occur in South Devon and Cornwall ". 



Samples collected by me last year in the underground workings 

 have yielded additional evidence which is of some interest. 



A sample weighing 157 grammes was treated with dilute 

 hydrochloric acid and yielded 3*1 per cent muddy residue and 

 - 32 per cent sand. The latter consists chiefly of quartz, up to 

 2'1 mm. diameter, the larger grains being well rounded. There is 

 also a fair amount of felspar, mainly orthoclase, and of muscovite 

 and glauconite, as well as a little flint. 



The sandy material was treated with bromoform, and the heavy 

 residue was found to amount to 0*012 per cent of the stone. Coarse 

 red and black grains are conspicuous in it. The former consist of 

 limonitic matter, and the latter were tested in borax beads on the 

 supposition that they might contain manganese. The beads, 

 however, showed the fine green colour, somewhat yellowish in 

 the oxidizing flame, characteristic of chromium. On crushing the 



' Cretaceous Rocks of Britain, vol. ii, 1903. 



2 Ibid., pp. 509, 513. 



3 Ibid., p. 545. 



