THE GEOLOGY OF TYTHERINGTON AND GKOVESEXD. 15 



careons matrix. At other times it is a yellowish argil- 

 laceous and magnesian limestone, with comparatively small 

 brecciated fragments of Mountain Limestone. I have found 

 it exceedingly confusing to students to call this variable 

 deposit by the common name of Dolomitic Conglomerate. 

 And I therefore venture to suggest that the beds under- 

 lying the Keuper Marls, and resting on the Palaeozoic rocks 

 in our area, should be called the Basement Beds of the 

 Keuper, or Basement Beds of the Trias. 



In the district under consideration, and in the section I 

 have been describing, the variable nature of these Basement 

 Beds is well exemplified. In the barton of Mill Farm the 

 grit is overlain by a ferruginous limestone. In Sub-section 

 2, after the reversed fault, the Basement Beds consist of 

 yellow marls, with bands of hard argillaceous limestone. 

 An analysis of this limestone gives only 8'41 per cent, of 

 argillaceous residue after treatment with dilute acid. Of 

 magnesium carbonate there is 9*13 per cent. 



On emerging from the Tytherington tunnel, Triassic beds 

 are again seen resting in the main on the oolitic beds of the 

 Carboniferous Series. They consist of red and 3^ellow marls 

 with bands of argillaceous limestone. In the quarry w^hicli 

 Mr. Hardwicke is now working in the oolitic beds, the Base- 

 ment Beds are freshly exposed. There is a blue argillaceous 

 limestone (which, after treatment with acid, leaves a sandy 

 residue) near the base, followed by red, yellow, and greenish 

 blue marls, with bands of argillaceous limestone. 



Beyond the Grrovesend tunnel (Sub-section 5) the Basement 

 Beds put on a wholly different character. They consist of a 

 brecciated conglomerate, with pebbles of milky Quartz, 

 derived from the Old Hed conglomerate on which they rest, 

 with occasional angular fragments of Mountain Limestone, 

 the whole cemented in a red ferruginous and argillaceous 



