pnrt 3] CHELLASTO>~ GYPSUM BRECCIA. 189 



stone between the pillars occurs right up to the top of the latter : 

 that is, to the roof of the deposit as developed at Woodlands 

 and Aston Glebe. Nor is there any sign of a similar action in 

 the Xewark district ; and it appears to me inconceivable that 

 beds of such regular thickness and such large area could be pro- 

 duced by this means. The extrusion of a corresponding quantity 

 •of Keuper Marl would necessitate the regular vertical uplift of 

 several feet of strata, in each case over many square miles. 

 Again, the intervening beds of marl are often still gypsiferous. 

 Also two or three beds may be quite close one to the other, 

 whereas at other times a thin bed may be overlain by a fairly 

 thick mass of still highly gypsiferous marl. 



The theory might be seriously entertained if the layers of 

 gypsum were frequently oblique to the stratification of the marls, 

 ( r if the extrusion of the matrix had been highly irregular. 



Other objections might easily be raised ; but, since these beds 

 rarely exceed a foot in thickness, Goodchild might have allowed 

 that they are original. If so, we might enquire why they have 

 not been thickened by downward percolation, seeing that the 

 gypsiferous marls bear a strong similarity to those of the Eden 

 Valley. The deposits have been described by Mr. A. T. Metcalfe, 

 who considers them to be the deposits of a saline inland sea. 1 



In the Carlisle district GoodchikVs theory can be applied only to 

 the top bed of gypsum, for he does not suggest that the downward- 

 moving gypsum can be converted into anhydrite in the process. 

 This will leave the lower 14 feet of the seam to have been formed 

 by original deposition, or in some other way. As above stated, the 

 lower bed of gypsum is split into two by the inclusion of a central 

 rib of coarsestone, which should be deprived of its gypsum if the 

 lowest part of the seam were due to downward percolation. On 

 the contrary, however, there is evidence that the gypsum, in either 

 coarsestone or foulstone, both in this and in other districts, is 

 partly secondary and derived from the pure seams. 



The occurrences at Kirkby Thore and Temple Sowerby give no 

 support to the percolation theory, which Burns condemns as being 

 quite untenable upon dynamical grounds alone. 2 Goodchild refers 

 to the disturbed nature of the beds immediately above the seams 

 in the Eden Valley as evidence in favour of his theory. The 

 disturbance, however, appears to be due to solution of the top of 

 the gypsum by subsoil waters in recent times (p. 185). 



In the Purbeck deposit of the Weald there is not the slightest 

 evidence of secondarv additions. The seam is one of original 

 deposition, the gypsum having been laid down continuously with 

 the ordinary sediments in alternating layers, as a rule ; although 

 in places a ' pot ' of gypsum occurs from which sediment was 

 excluded at the time of deposition, but not pushed aside by a 

 subsequent segregatory process. 



1 : The Gypsum Deposits of Nottinghamshire & Derbyshire ' Trans. Notts 

 Xat. Soc. 1894 ; and Trans. Inst. Min. Eng. vol. xii (1896-97) pp. 107-14. 



2 ' The Gypsum of the Eden Valley ' Trans. Inst. Min. Eng. vol. xxv (1902- 

 1903) p. 414. 



Q. J. G. S. Xo. 29-3. y 



