1850.] R. N. MANTELL ON THE OOLITE OF WILTS. 313 



Trowbridge station-yard is excavated out of this rock. A slight 

 fault runs across the line at the point where the booking-office now 

 stands, and the same displacement is visible half a mile off on the side 

 of the turnpike road to Bradford. The Cornbrash continues very level 

 to about the middle of the next cutting, where a displacement of consi- 

 derable extent brings down the Oxford clay, which continues only for 

 6 chains, where another fault replaces the Cornbrash, which dips south 

 rapidly, so as to disappear almost immediately. The Oxford clay Hes 

 on the Cornbrash, and a few chains further on we find a stratum of 

 sandstone and sand representing the Kelloway rock. This too extends 

 but a short distance, and the next cutting at Studley (10 miles, 20 

 chains) brings to light the bituminous unctuous shales of the Ox- 

 ford clay*. This excavation is about 13 chains long, and 23 feet at 

 its greatest depth ; from it I obtained beautiful specimens of Belem- 

 nites and Belemnoteuthis. 



^ The whole thickness of the shales exposed by this cutting is about 

 forty-five feet, and were we to restore them to their original horizon- 

 tal position, we should have the following sequence, commencing with 

 the beds that would be the uppermost of the series. 



Two feet of drift, which covers the surface everywhere, in some 

 places to the depth of six or eight feet, — and is sometimes difficult 

 to distinguish from the decomposed Oxford clay, being of the same 

 yellow colour. Contains a few elephant's teeth. 



Three feet of crumbly shaly marl, containing Serpula vertebralis. 



Five feet of shaly marl, with Belemnoteuthides in abundance. 



Nine feet of very strong slaty clay, containing about midway a layer 

 of pyritical Septaria and numerous Belemnites, Belemnoteuthides^ 

 and Ammonites. 



Two feet of thinner slaty clay, with quantities of Rostellarice and 

 drift wood. 



One foot of rock, in which the Ammonites Reginaldi chiefly oc- 

 curred. 



Five feet of thick slaty clay, containing Belemnites^ Ammonites^ and 

 lignite : Belemnoteuthis rare. 



Three feet of crumbly stone. 



Two feet of very strong clay, with but a few fossils. 



Five feet of thick slaty clay, containing Belemnites, Belemnoteuthides^ 

 Ammonites Jason, and lignite. 



Ten feet more of clay was exposed, but being intersected where it 

 cropped out, it was decomposed and crumbly from the effects of 

 the atmosphere. 



Lignite occurs in most of the beds, and frequently with ostrece at- 

 tached. In one place a flattened tree twelve feet long was used in 

 situ for some time as part of a barrow-run ; so little was its vegetable 

 structure and its strength and tenacity impaired, though the tree 

 must have been coeval with the extinct belemnites with which it was 

 buried. Much of the wood, especially the curious bed of lignite 



* This clay emits a brilliant gas when burnt, and I have frequently used it to 

 illuminate my room. 



