120 Br. R. L. Sherlock — Datum-lines in Englisli Kewper. 



considered more than a working hypothesis until the physical 

 difficulties are met. If it can be shown that compression is not 

 required, and that the phenomena of folded mountain chains can be 

 otherwise explained, a distinct advance would be made in dynamical 

 geology. 



IV. — Datum-lines in the English Keupek. 

 By E. L. Sheklock, D.Sc, A.E.C.Sc, F.G.S. 



IN the almost complete absence of fossils in the British Keuper 

 there has been a lack of datum-lines in that formation by which 

 we may compare the horizons of different sections. Yet in such 

 a thick and widely spread deposit it is very desirable to have sub- 

 divisions enabling us to give the particular part of the Keuper to 

 which a section belongs. In deposits such as the New Red 

 formations too great stress has been laid on lithology, inevitable 

 perhaps in the scarcity of fossils, but a source of grave errors in 

 correlation. Tor example, Mr. L. J. Wills' thinks that fossils found 

 in the Keuper of Warwick have affinity, not with the Keuper, but 

 with the Muschelkalk of Germany. Again, there are strata in the 

 Permo-Bunter of Nottinghamshire^ which might be mistaken for 

 Keuper Waterstones, if only lithology was considered. Over small 

 areas a band of sandstone with some peculiarities may be used as 

 a datum-line, as in the Arden district of Warwickshire^ and in 

 Nottinghamshire,* but these are of local value only. 



Eecently Mr. Bernard Smith and myself have had occasion to visit 

 all places where gypsum is worked, or likely to be workable, 

 throughout England, and it appears that the workable deposits of 

 gypsum within the Keuper occur at definite horizons. The economic 

 results have been published in a recent memoir,* but I wish here to 

 show that they give us two definite horizons, the upper one found at 

 intervals between North Yorkshire and Somerset and the other over 

 parts of three Midland counties. Using these datum-lines, I propose 

 to show that they help us to state the nature of the Keuper— Rhsetic 

 junction and to determine whether or not the Tea-green Marls occur 

 at a definite horizon. 



1. The Upper Horizon. — Eour beds of gypsum occur in a definite 

 order in the quarries and mines situated between Beacon Hill 

 (Newark) and Orston, to the south-west, a distance of 9^ miles. In 

 the figure sections are given of the strata found at Newark, Hawton, 

 Bowbridge, and Orston. Those at Newark, Bowbridge, and Orston 



^ "On the Fossiliferous Lower Keuper Books of Worcestershire": Proc. 

 Geol. Assoc, vol. xxi, p. 268, 1910. 



^ R. L. Sherlock, " The Ilelationship of the Permian to the Trias in 

 Nottinghamshire": Quart. Journ. Geol. Soc, vol. Ixvii, p. 82, 1911. 



^ C. A. Matley, " The Upper Keuper (or Arden) Sandstone Group and 

 Associated Eocks of Warwickshire": Quart. Journ. Geol. Soc, vol. Ixviii, 

 pp. 2-52-80, 1912. 



* B. Smith, "The Upper Keuper Sandstones of East Nottinghamshire " •' 

 Geol. Mag., 1910, pp. 302-11. 



* E. L. Sherlock &. B. Smith, Special Reports on the Mineral Resources of 

 Great Britain (Mem. Geol. Surv.), vol. iii, " Gypsum and Anhydrite," 1915. 



