part 3] THE CHELLASTON GYPSUM BRECCIA. 177 



sea-water, or of a given body of fresh water. We should rather 

 anticipate a varying set of conditions upon which changes might 

 be rung. 



All this was in general admitted by J. G-. Goodchild, but he 

 was doubtful whether the exact balance between the influx of 

 water into closed basins and the subsequent evaporation of that 

 water could have been maintained for a sufficiently long period 

 to admit of the uninterrupted precipitation of such masses of 

 sulphate of lime as occur in our red rocks. He says l that 



' All the facts brought to light by a study of the closed basins of the present 

 day testify to the view that such forms of deposition are very exceptional. 

 Instances are. in fact, unknown .... Variations in salinity have been the 

 rule, and not the exception. In all of them the prevailing mode of occurrence 

 of the chemical precipitates is that of thin sheets — varying from a few inches 

 in thickness to mere films of disconnected spangles — which are interleaved 

 with a succession of sedimentary deposits brought in by freshets.' 



Without going farther into the matter for the moment, we may 

 recall that thick masses of the Mag-nesian Limestone of Xotting-- 

 hamshire and Yorkshire appear to have been formed exclusively 

 of chemically-precipitated rhombs of dolomite, accumulated as a 

 dolomite-sand in which false bedding is developed on a large scale.- 



In the spring of 1915, Dr. R. L. Sherlock and I examined 

 practically all the important worked deposits of gypsum in this 

 country, and it was my fortune to come across a breccia of an 

 interesting type, which will now be described. 



II. The Chellaston Bkeccia axd Associated 

 Sedimexts. 



The rock is exposed in the Chellaston Alabaster Quarries (the 

 sole representative, in this Derbyshire village, of a long series of 

 excavations that furnished the material for some of the finest 

 monumental work in the country 3 ) worked by Messrs. H. Forman 

 & Son, to whom thanks are due for offering both time and 

 information so liberally (see map, fig. 1, p. 176). 



The gypsum occurs as a series of ' pillars,' sometimes almost or 

 quite in contact, but usually separated by ' coarsestone ' and 

 ; foulstone,' the former consisting of more gypsum than marl, 

 the latter of more marl than gypsum. 



These pillars are nearly circular in plan, except when they abut 

 one against the other, when they may be roughly polygonal. They 



1 ' Some Observations upon the Natural History of Gypsum ' Proc. Geol. 

 Assoc, vol. x (1887-88) p. 442. 



2 'Geology of the Country around Ollerton ' Mem. Geol. Surv. 1911, 

 pp. 12-13. 



3 See ' Special Reports on the Mineral Resources of Great Britain : 

 vol. hi — Gypsum & Anhydrite' Mem. Geol. Surv. 1915, p. 17. In this 

 volume also accounts will be found of most of the mines and quarries men- 

 tioned in the present communication. See also A. T. Metcalfe, ' The Gypsum 

 Deposits of Nottinghamshire & Derbyshire ' Trans. Inst. Min. Eng. vol. xii 

 (1896-97) pp. 107-14. 



