188 MR. B. SMITH ON THE [vol. lxxiv, 



Mr. A. T. Metcalfe states that, in the portions of the strata 

 immediately surrounding a large ' ball ' in the Newark district, 

 gypsum 



' sometimes appears to be altogether absent, as though it had been drawn 

 away to form the " ball " by a concretionary process.' ] 



Groodchild claims to have seen many cases in Cumberland, as well 

 as in Staffordshire and Westmorland, where the original bedding 

 of the marls can be distinctly traced through nodules of gypsum, 

 and he deduces that the nodules have grown by secretion in situ. 

 and have displaced the marls. 2 



While we may admit that a limited amount of secondary secretorv 

 action may have taken place at times, it seems more likely that 

 the segregatory action was original ; especially when we remember 

 that traces of bedding are visible in the original red gypsum of 

 the Chellaston pots (pp. 179, 181). 



V. ' Downward Percolation ' Theory. 



Groodchild, as mentioned above (p. 177), states that the prevailing 

 mode of 'occurrence of gypsum, at the present day, is that of thin 

 sheets interleaved with a succession of sedimentary deposits; and, 

 after many years of experience and on mature deliberation (oj). 

 supra clt. p. 442), he expressed the opinion that most, if not all, 

 of our British deposits of gypsum 



' seem to represent numerous episodes of higher salinity in the history of 

 the old inland lakes — the normal periods, or those of lower salinity, being 

 represented by the ordinary form of sediment present in those rocks." 



Up to this point we are in agreement. He goes on to say, 

 however, that the sulphate of lime diffused throughout the 

 sedimentary strata was to some extent dissolved by subse- 

 quent infiltration and transported to lower levels, 

 where it has been concentrated in more or less nodular, or 

 even as stratiform, masses, there being at the same time a gradual 

 displacement of the beds around. The deposit grows by further 

 additions, extruding a corresponding quantity of the matrix as it 

 does so. 



Exception must be taken to this explanation of the formation 

 and growth of the beds of gypsum, for there is little field evidence 

 to uphold the theory, which has already been challenged by the 

 late J). Burns. 3 



At Chellaston there is no sign whatever of addition to the seam 

 from above at a date subsequent to deposition; for, to take only 

 one point, the horizontally-bedded and practically undisturbed foul- 



1 ' The Gypsum Deposits of Nottinghamshire & Derbyshire ' Trans. Inst. 

 Min. Eng. vol. xii (1896-97) p. 109. 



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

 Assoc, vol. x (1887-88) p. 435. 



3 'The Gypsum of the Eden Valley' Trans. Inst. Min. Eng. vol. xxv 

 <1902-1903) p. 414. 



