896 A. Strahan — Lower Keujjer Sandstone. 



II. — On the Lower Keuper Sandstone of Cheshire. 

 By A. Strahan, M.A., F.G.S., H.M. Geological Survey. 



WHILE I was engaged in surveying the Drift-deposits of the 

 neighbourhood of Warrington, Euncorn, and the Peckforton 

 Hills near Chester, my attention was called to what appeared to 

 be a good boundary-line in the middle of the Lower Keuper 

 Sandstone, separating the Waterstones from the Conglomerates 

 vinderlying them. The sections at Euncorn and Frodsham, where 

 I first saw this line exposed, have been already described with 

 many others in the Survey Memoirs on the Neighbourhood of 

 Prescot (3rd edition) and on the Neighbourhood of Chester. They 

 showed that there was no passage from the Waterstones down into 

 the Conglomerates, but that there was on the contrary a sharp 

 division between them ; and as on following this line further south, 

 I found that it was persistent, and everywhere separated beds of a 

 very different nature, it was decided that it should be engraved on 

 the Map, the new classification of the Keuper of this neighbourhood, 

 as contrasted with the old, being shown in the accompanying figure. 



The Lower Keuper Sandstone or Basement Beds consist of quartz- 

 ose sandstones with a sharp and rather coarse grain, conglomeratic 

 or brecciated in parts and always current-bedded. The bold and 

 craggy escarpment formed by the suj)erposition of these beds on 

 the soft Upper Mottled Sandstone of the Bunter often presents 

 minor features or terraces, resulting from the separation of the 

 harder building stones into courses by partings of softer material. 

 These partings ai-e occasionally formed by a bed of shale, but more 

 usually by a very soft current-bedded mottled sand, of a finer grain 

 than the building stone. The upper part of the subdivision consists 

 of a considerable thickness of this soft sand, as is seen in the Eailway 

 Cutting at Frodsham (Geology of the Country around Prescot, 

 Fig. 4), where the current-bedding is on so large a scale as to have 

 been sometimes mistaken for contortion. The beds are arranged 

 in the foi'm of troughs, one within another, and inclined towards 

 the east at a high angle. In the section these troughs are cut across 

 nearly at right angles, so as to present arcs of a number of nearly 

 concentric circles of about 40 yards diameter. For convenience 

 of reference, I gave to these beds the name of the Frodsham Beds. 

 They are persistent over this part of Cheshire, but variable in thick- 

 ness. In the lower part of the Frodsham Beds, the coarser-grained 

 and harder sandstone comes in gradually, often appearing first in 

 lenticular masses, so that there is a perfect passage downwards. 



Every course of the harder sandstone is as a rule conglomeratic 

 and brecciated towards its base, and rests on a slightly eroded 

 surface of the underlying bed. Fragments of shale often occur 

 in irregular lines in the brecciated portion, as though a bed of 

 shale, previously laid down and half hardened, had been torn up 

 and the fragments rolled about, though not moved to a distance. 

 In this respect, and in the frequent repetition of lines of erosion, the 

 Lower Keuper Sandstones resemble those of the Coal-measure age. 



