82 ME. R. L. SHERLOCK ON THE RELATIONSHIP OF THE [Feb. I9II, 



sandrock. These strata bear a close resemblance to the Keuper 

 "Waterstones of Nottinghamshire. A well, sunk by the railway 

 company near the mouth of the tunnel, proved the presence of the 

 Magnesian Limestone at a depth of 15 feet below the rails. 



The tunnel itself is bricked up, but the section is continued at its 

 northern end. Here the marly beds, seen at the bottom of the 

 cutting at the southern end of the tunnel, have been brought by 

 the gentle dip of the strata to the top of the section. Much of this 

 cutting is unfortunately obscured by grass ; but the constant oozing- 

 of water from the beds causes landslips, and thus it is possible to 

 make out clearly the whole of the succession. 



The marly sandrock of the Lower Mottled Sandstone passes 

 downwards into the red ' Permian Marl ' by an increase in the 

 thickness of the marly partings and a corresponding diminution of 

 the h'ne-grained flags, which eventually come to be represented only 

 by the ' skerries ' of the Permian Marl. No true boundary can be 

 traced between the Permian Marl and the Lower Mottled Sand- 

 stone ; but, for the purpose of mapping them, an arbitrary line was 

 taken below the last considerable sandy lenticular band. 



Thus defined, the Permian Marl has a thickness of about 13 feet 

 only. It rests upon the Magnesian Limestone without visible un- 

 conformity, but with a sharp lithological break. At the mouth of 

 the tunnel the top of the limestone is 4 feet above the rails, and 

 the low dip of about 1° brings it to the surface of the ground 

 400 yards from the tunnel. A little farther on the cutting forks,, 

 and both branches show good sections of the limestone. The right- 

 hand branch (the Great Northern) turns northwards and becomes 

 parallel to the strike of the beds, so that the section remains in the 

 same part of the limestone ; but the left-hand branch, which carries 

 the Great Central main line, turns westwards and cuts through 

 practically the who]e thickness of the Magnesian Limestone : 

 the grey marls with fossiliferous limestones, which form the 

 lowest division of the Permian here, cropping out a little beyond 

 the end of the cutting. 



The Midland Railway crosses over the Great Central, hence the 

 sections on the Midland are in slightly higher strata than those 

 on the Great Central. Commencing as before in the south, we find 

 that the lowest beds exposed along the Midland line consist of 

 the red sandrock seen close by at the top of the other cutting. Pro- 

 ceeding northwards, the rise of the land-surface causes a deepening 

 of the cutting and brings in increasingly higher strata, until, at 

 the tunnel entrance, we see at the top rather massive and coarse 

 reddish sandrock, which is almost the highest bed of the Lower 

 Mottled Sandstone, for the summit of the hill is in the Pebble Beds. 



At the northern end of the Midland tunnel the sections are a 

 repetition of those exposed at the southern end. 



These sections are of great importance, because the Permian Marl, 

 which is seen to pass upwards by imperceptible stages into the 

 Bunter, is not, as one might expect, the highest bed of the Permian 

 System, but is the Middle Permian Marl, that is, the marl which 



