part 3] CHELLASTON GYPSUM BRECCIA. l201 



lying isolated, or nearly isolated, masses of soft gypsum rilling 

 depressions or ' pots ' in the Keuper Marl. 



3. By comparison with this deposit, and also by independent 

 •evidence, it seems probable that the greater number, if not all, 

 of the important beds of gypsum in this country were deposited 

 as gypsum and have never been in the anhydrous condition. They 

 have behaved throughout as stratiform deposits, and have suffered 

 internal movements, nearly contemporaneous with their formation, 

 similar to those that have occurred elsewhere in semi-consolidated 

 laminated silts and sandstones of various geological ages. 



•A. When anhydrite is present, the balance of evidence favours 

 the view that it is original, and was deposited in a stratiform manner, 

 in sequence with gypsum, the deciding factors being chiefly tem- 

 perature and concentration of solutions. When il, occurs in the 

 middle of balls of gypsum, both minerals are, in part, segregations. 



5. Microscopic evidence furnishes proof that there has been in 

 some cases an alteration of anhydrite into gypsum. This alteration, 

 however, is considered to have occurred at the time of deposition, 

 and to be confined to the existing plane of contact between the 

 two, minerals. 



6. In this country no case has been made out for the conversion 

 of a bed of limestone into gypsum. 



7. Fibrous gypsum is nearly always of secondary origin, and has 

 been formed, whenever the opportunity offered, from the date of 

 •deposition of the gypsiferous beds down to the present day. 



X. Bibliography. 



1686. Plot, R.— 'The Natural History of Staffordshire.' 



1879. Roth, J. L. A. — ' Allgemeine & Chemische Geologic ' vol. i, pp. 463-90. 



1883. Hammeeschmidt, F. — ' Beitriige zur Kenntniss des Gyps- & Auhydrit- 

 Gesteines ' Tscherm. Min. Petr. Mitth. vol. v, pp. 275-79. 



1888. Goodchild, J. G. — ■" Some Observations upon tiie Natural History of 

 Gypsum' Proc. Geol. Assoc, vol. x, pp. 425-45. 



1894. Metcalfe, A. T. — 'The Gypsum Deposits of Nottinghamshire & Derby- 

 shire ' Trans. Notts Nat. Soc 



1898. Metcalfe, A. T. — 'The Gypsum Deposits of Nottinghamshire & Derby- 

 shire ' Trans. Inst. Min. Kng. vol. xii, pp. 107-14. 



1903. Burxs, D.— ' The Gypsum of the Eden Yallev ' Trans, In^t. Min. Eng. 

 vol. xxv, pp. 410-28. 



1903. Geikie, Sir Archibald. — 'Text-Book of Geology ' 4th edit. vol. i. 



1906. Tk.vfford Wyxxe, T. — ' Gypsum, & its Occurrence in the Dove Valley' 



Trans. Inst. Min. Eng. vol. xxxii, pp. 171-84. 



1907. Losias, J. — -'Desert Conditions & the Origin of the British Trias' Proc. 



Liverpool Geol. Soc. vol. x, pp. 172-97 ; and Geol. Mag. dec. 5, vol. iv, 

 pp. 511-14, 555-63. 

 1907. Kemp, W. J., & Lewis, G. A. — ' Gypsum in Sussex ' Trans. Inst. Min. Eng. 

 vol. xxxiii, pp. 449-72. 



1909. 'The Geology of the Melton Mowbray District ' Mem. Geol. Surv. 



1910. S.mith, B. — 'The Upper Keuper Sandstones of East Nottinghamshire' 



<Teol. Mag. dec. 5, vol. vii, pp. 302-11. 



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

 1911. Jukes-Browne, A. J. — ' The Building of the British Isles ' 3rd ed. 



1911. Wade, A. — 'Some Observations on the Eastern Desert of Egypt, &c. ' 



Q.J.G. S. vol. lxvii, pj). 238-61. 



1912. Kramm, H. E. — ' Gvpsum of New Brunswick' Suinm. Rep. Geol. Surv. 



Canada for 1911, pp. 322-27. 



