176 



THE PERMIAN SALT LAKE. 



COSMO JOHNS, M.I.Mech.K., F.G.S. 



That the Permian rocks east of the Pennines differ from their 

 representatives in the west is a well known fact. That they 

 were deposited in an inland sea under conditions unfavourable 

 to animal life has loni^ been recos^nised. The peculiar character 

 of the deposits, that is, so far as this island is concerned, and the 

 evidently abnormal conditions attending their deposition, render 

 them deserving of far more attention than they have received. 

 In a short paper like this a detailed discussion of the many 

 interesting features presented would be out of place, if not 

 impossible, so its scope will be limited to a study of the climatic 

 and other conditions that must have prevailed during the time 

 the upper marls were being laid down. 



The particular section of the upper marls to be discussed is 

 that furnished by the core of the well known South Carr * or 

 Haxey deep boring. In the greater portion of the Midland 

 coalfield the Trias overlaps the upper marls which were laid 

 down in the shrunken relic of the great Permian Sea. The 

 eastern representatives of the Permian rocks carry in their 

 changing features, as we examine them as an ascending series, 

 every evidence that the sea in which they were deposited had not 

 only become land-locked, but that evaporation was proceeding 

 apace and increasing salinity was accompanying the decreasing 

 volume as might naturally be expected. In upper marl time the 

 dwindling sea had become a veritable salt lake — not only salt, 

 but saturated with salt — the evidence for which will now be 

 discussed. 



Towards the top of the upper marls we find a thin bed of 

 gypsum, and above it, but separated by more marl, a bed of 

 anhydrite 9 feet in thickness. This anhydrite is remarkably 

 pure and, so far as can be seen,t its formation was not inter- 

 rupted by any sediments coming in. This very pure bed is 

 followed by marls, then comes another thin gypsum band. A 

 little marl follows, and then the Triassic sandstone appears. 

 There are good reasons for believing that this bed of anhydrite 

 extends over a fairly large area of the coalfield, but it is probably 

 not continuous with the thick deposit which lies at the top of the 

 Permians at Hartlepool, :[ The sequence is complete, and the 



* Trans. .Mainlicster (leol. Soc. 1902, p. 5S. Trans. Fed. Inst. M.E. 

 vol. xii. i<S()7, ]). 5i<S. 



t Private conimunication to aullior. 



;}; Geikic, 'Text Hook of Gcolojcy," 1903, p. 1071, footnote. 



Naturalist, 



