Miss Eyton — On Glacio-Marine Denudation. 545 



In tiie tMrd cutting the Chalk-rock occurs at a less elevation, so 

 that a smaller section of the Lower Chalk is seen beneath it ; and 

 in the fourth cutting, immediately adjoining the village of New Mill 

 End, it occurs at the bottom of the excavation, which in the deepest 

 part is about ten or twelve feet. This formation also occurs in the 

 immediate vicinity of Luton, on the opposite side of the valley of 

 the Lea. It has been met with in two Chalk-pits now closed, 

 in one of which, near the London Eoad, it was customary to 

 sink a shaft down to this bed, and then excavate a considerable 

 chamber beneath, the Chalk-rock forming an excellent roof to the 

 workings. 



Through the kind assistance of K. Etheridge, Esq., Palseontologist 

 to the G-eological Survey, I am enabled to add the following species, 

 from the Totternhoe stone, to the list published in the April Number 

 of the Geological Magazine (p. 159) : — • 



Rhynchonella plicatula. 

 „ Cuvieri. 



,, oetoplicata. 



Exogyra. 

 Palceastacus, 

 Plesiosaurus campylodon. 



VI. — On the Glacio-Marine Denudation of certain Districts. 



By Miss Eyton. 



HAVING been for the last twelve months engaged in a careful 

 study of the post-Tertiary geology of the eastern part of Shrop- 

 shire, I have at length arrived at the conclusion that the denudation 

 of the New Eed Sandstone in this neighbourhood, and consequent 

 excavation of the Tern basin, has been effected partly by glacial and 

 partly by marine agency ; the grounds upon which this conclusion 

 is based being: — (1) An attentive consideration of the general form 

 and outline of the basin ; (2) A particular examination of the drift 

 beds contained therein. 



First, with regard to the general outline. The district drained by 

 the river Tern, forms a basin of extensive area, but with a compara- 

 tively narrow outlet. The area is almost entirely of New Eed 

 Sandstone, chiefly the Lower Biinter beds, bounded on the east 

 by the basaltic rock of the Wrekin range of hills, and by the long 

 line of low Coal-measure hills extending through Ketley, Donning- 

 ton Wood, and Lilleshall, in the direction of Staffordshire. In fact, 

 as will be seen by consulting the Ordnance map, the outline of the 

 basin is here co-extensive with the line of fault separating the 

 Biinter Sandstone from the Coal-field. On the opposite side of the 

 latter there occurs another great fault, dividing the Coal from the 

 Permian beds, and by sinking a shaft through the latter, the Coal 

 was again found on the lower side of the fault. It is extremely 

 probable that the same experiment might be attended with similar 

 success in the Tern basin. Indeed, there can be little doubt that, 

 before the period of volcanic convulsion, which occasioned the faults, 

 both the Permian and lower Biinter beds covered the whole of the 

 Shropshire Coal-field, and it is probable that even since that period 



VOL. IV. NO. XLII. 36 



