400 A. Sfrahan — Loiver Keuper Sandstone. 



as occurring about midway between the areas in Cheshire and near 

 Nottingham, where the sequence has been clearly made out. 



This line therefore appears to be persistent over a large area, and 

 to form a strong separation of the Waterstoues from the Keuper 

 Basement Beds, even in localities where it was formerly supposed 

 that there was a perfect passage between the two. While surveying 

 in Cheshire, I found that in consequence of the prevalence of shales 

 in the Waterstones in certain districts, they were included in the 

 Keuper Marls, while close by they were mapped as Lower Keuper 

 Sandstone, in consequence of the exposure of sandy beds in them. 

 The upper boundary of the Lower Keuper Sandstone therefore did 

 not follow one horizon, but was taken across the strike of as much 

 as 200 feet of strata. In consequence of this, it was supposed that 

 there was a perfect passage between the Waterstones and the Base- 

 ment Beds in those localities where it is now known that a sharp 

 line of separation exists. 



At this horizon, moreover, the principal overlap in the Trias takes 

 place, for while the Bunter and the Keuper Basement Beds, which 

 are confined approximately to the same limits, thin out along a line 

 drawn from north-east to south-west through Leicestershire (Triassic 

 Memoir, p. 60), the Waterstones, with the allied Marls, run beyond 

 this limit so as to rest directly on Paleeozoic rocks, the base of the 

 Waterstones becoming in such cases conglomeratic. A similar 

 overlap of the Marls has been noticed in Devonshire by Mr. Ussher, 

 who considers that at this period for the first time a connexion 

 was established between the Triassic waters of Devonshire and the 

 Midland Couuties.^ 



At this period also the change in the physical geography of the 

 region commenced, which led to the formation of the Eed Marls 

 with their associated beds of rock-salt and gypsum. The appearance 

 of the casts of salt-crystals for the first time in the Waterstones, 

 taken in connexion with the uniformly even-bedding, lamination 

 and loamy texture of these beds, points to their having been laid 

 down under conditions totally different from those which produced 

 the sands and conglomerates of the Bunter, and of the Lower 

 Keuper Sandstone. During the period of the Bunter shifting 

 currents must have prevailed, sweeping along from the north (as 

 shown by Prof. Hull) between the hills of Derbyshire and of Wales 

 large quantities of sand and gravelly sediment. The same or 

 similar currents prevailed during the deposition of the Lower 

 Keuper Sandstone, which is not only lithologically similar to the 

 Bunter, but follows it also in its geographical range and development. 

 But after this period, the free circulation of currents ceased, for all 

 the succeeding beds show clear evidence of having been deposited 

 in tranquil water, while the pseudomorphs of rock-salt prove that 

 this water occupied a land-locked basin, in which concentration of 

 brine was taking place. These conditions, appearing for the first 

 time at the base of the Waterstones, prevailed without intermission 

 until the close of the period of the Eed Marls. 



1 Quart. Journ. Geol. Soc. Aug. 1878. 



