Geology of Wiltshire. 319 



Fossils pbom the Fullee's Eaeth, ^r*. 



Pholadomya lyrata. Sow. Ostrea grcgaria. Sow. 



Modiola gibbosa. Sow. Avicula echinata. Sow. 



,, Hillana. Sow. Ehynconella concinna. Sow. 

 Goniomya augulifera. Sow. ,, media. Sow. 



Lima duplicata. Sow. Acrosalenia spinosa. Agas.* 

 Ostrea accuminata. Sow. 



Great Oohte. 



This formation, marked g', is capable of being divided into two 

 well-marked zones or stages — similar to those which have been 

 shown to exist in the neighbourhood of Cheltenham, and extending 

 eastward into Oxfordshire^ : — the lower zone, which comprises the 

 Stonesfield slate ; and the upper, of which the typical section occurs 

 in this sheet at Sapperton Tunnel. 



Lower Zone. 



At the base of the Great Oolite, along the margins of Stroud 

 and Nailsworth valleys, a few inches or feet of brown sandy slates 

 with partings of clay may frequently be observed, which probably 

 represents the Stonesfield slate of E3'eford and Sevenhampton, 

 although the chaiacteristic fossil Trigonia impressa is wanting. 

 This is surmounted by from 20 to 40 feet of white shelly oolite, 

 in which false bedding is prevalent, being, indeed, a characteristic 

 feature of this zone. The fossils are very abundant, as has been 

 shown by Mr. Lycett, but they are generally in a fragmentary 

 state, and give evidence of having been drifted by currents. 



These beds furnish the valuable " Bath freestone," which near 

 Corsham is worked underneath the Forest marble by means of 

 vertical shafts and tunnel work."^ ^ One of these at Lower Pickwick 



• In the excavation of a portion of the Box tunnel, the beds of the Fuller's Earth were reached 

 and great quantities of it were drawn up one of the shafts and spread on the " spoil bank," on the 

 top of the hill. This afforded a grand opportunity for studying the fossil forms which are abundant 

 in some of the beds. And even at the present time many specimens may be obtained among the 

 bushes with which the banks are overgrown. 



' See Memoirs of the Geological Survey,— Geology of Cheltenham, p. 53, 

 et seq. 



^ It is probable that the greatest amount of mineral wealth in the county of 

 Wilts, is to be found in the Great Oolite — the "Bath Freestone." It is to be 

 hoped that the Pisolitic Iron Ore of Westbury, and the Lower-Green-Sand Ore 



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