x. MARLSTONE GROUP. 115 



be followed step by step in a belt of picturesque buttresses on the 

 western front of the high oolitic region, from the vicinity of Bath, 

 by Wotton-under-Edge, Gloucester, and Cheltenham, to Broadway 

 Hill. Turning round to the east and south, it descends the Vale 

 of the Evenlode, and afterwards holds a picturesque course by 

 Long-Compton to the crest of Edgehill and the plain of Banbury. 

 Here it returns down the valley of the Cherwell, and was observed 

 distinctly about Rowsham and Steeple-Aston by W. Smith in 

 1805. After this, through a more undulated country, it passes 

 by Daventry towards Belvoir and Grantham, beyond our limits. 



It is a mass ten, twenty, or forty feet thick, formed in some- 

 what irregular, often thin beds, which are traversed by joints as 

 in the oolites. All the associated beds counted, the total thickness 

 in the vicinity of Cheltenham is stated to be 115 feet. Carbonate 

 of iron is diffused through the whole, giving it a brown aspect 

 where air and water have had access ; but the stone is often blue 

 in the central parts. Some beds are richly charged with rhyn- 

 chonellae, terebratulse, belemnites, and ammonites ; but in con- 

 siderable tracts of country the fossils are not plentiful. It has been 

 opened for ironstone at Fawler in the Vale of Evenlode, and ex- 

 periments for the same purpose were tried at Worton and Steeple- 

 Aston. It often contains ten, fifteen, and twenty per cent, of iron. 

 The vicinity of Gloucester and Cheltenham, of Chipping-Campden 

 and Moreton, of Banbury and Edgehill, are good stations for 

 examining the marlstone. Nearer Oxford we have good exposures 

 at Rowsham and Steeple-Aston, where the strata above the rock 

 are very well traceable upward to the white oolite of Hopcroft's 

 Holt. Ammonites spinatus (A. Hawskerensis of Yorkshire) appears 

 to be one of the most characteristic fossils of this zone, for in this 

 district it must count as one, though in Yorkshire and Dorsetshire 

 it may be divided into several. 



The section from Rowsham to Hopcroft's Holt, as well as it can 

 now be seen, appears as under : 



Uppermost strata consisting of white calcareous rock, partially oolitic, with bivalve 

 shells. The great oolite 40 feet. 

 Marly clay, 5 feet. 

 Sands and sandstone, partly ferruginous, with Astarte minima, 13 feet. 



Memoirs of W. Smith, p. 61. 

 I 1 



