Correspondence — Mr. E. Wilson. 523 



coI^I^:E]s:po^^IDE3^o:E3. 



THE "LOWER KETJPER SANDSTONE" OR "BASEMENT BEDS." 



Sm, — While cordially agreeing with much that Mr. Strahan has 

 to say on the above subject, I would enter a strong protest against 

 the general line of argument which runs through his paper to 

 the effect that, in the Midland counties, the Basement Beds of the 

 Keuper are more closely connected stratigraphically as well as litho- 

 logically with the underlying Bunter sandstone than with the over- 

 lying members of the Keuper, and that the most important break in 

 the Triassic series comes at the base, not of the Basement Beds of 

 the Keupei', but of the Waterstones. In the counties of Nottingham, 

 Derby, and Stafford, the Keuper Basement Beds consist of a series 

 of white and red sandstones and conglomerates with irregular inter- 

 stratifications of red marl ; they are very variable in character and 

 thickness, never more than 50 or 60 feet, and often entirely absent. 

 On the east side of Nottingham the Keuper Basement Beds (when 

 present) rest on the Pebble Beds of the Bunter ; but four miles west 

 of the town, in Stapleford Hill (where by the way they are locally 

 well developed), and in Catstone Hill, they repose directly on the 

 Lower Mottled Sandstone of the Bunter. Here then we get decisive 

 evidence of an unconformable overlap of the Bunter Pebble Beds by 

 the Keuper Basement Beds, and the removal of at least 200 feet of 

 strata during the interval of time which separated those two groups 

 of rocks. 



Mr. Strahan cites the appearances of erosion of the Basement Beds 

 beneath the Waterstones in support of his theory of a great break at 

 that horizon, but denies that erosion of the rocks beneath the Base- 

 ment Beds is of any value as evidence of a break between the Base- 

 ment Beds and the Bunter. About three years ago I had the op- 

 portunity of examining the junction of the Keuper Basement Beds 

 and Waterstones, at Colwick Wood near Nottingham, for a distance 

 of over a hundred yards. In this section the (irregular) bedding 

 planes of the Basement Beds ran roughly parallel with those of the 

 Waterstones. At the top, though the junction line was quite even, 

 the Basement Beds certainly had the appearance of having suffered 

 denudation before the deposition of the Waterstones. In view how- 

 ever of the abundant evidences of contemporaneous erosion in the 

 Basement Beds, no importance can be attached to these appearances 

 as indicative of any considerable lapse of time between the two 

 series. The Waterstones and the Basement Beds were apparently 

 conformable. This conformability is equally evident in the district 

 of Alton, Staffordshire. 



It is true that, in parts of Notts and Derbyshire, the upper mem- 

 bers of the Keuper overlap the Keuper Basement Beds and rest on 

 the Bunter and older rocks, but we have good reason for believing 

 that this is simply a conformable overlap, for the Waterstones are 

 themselves also partially or wholly cut out by the rising surface of 

 the older underlying rocks. 



