MOLLUSCA FROM THE GREAT OOLITE. 5 



Fullers-earth. In another direction, one mile south-east of the town, is a marly band, 

 containing a dense colony of a species of Terebratula, which is likewise the sole fossil 

 observed. This isolation of the Terebratute is worthy of notice ; they occur but as a few 

 stray individuals in the shelly beds of the formation : in one instance, indeed, a shelly quarry 

 at Bussage, a little to the north of the vale of Chalford, contains a large assemblage of a 

 smooth, undescribed species, but at that place the other genera suddenly disappear, and the 

 TerebratulaB are either alone or accompanied only by a few small bivalve shells. The 

 Bradford clay, marked by the Terebratula digona, has not been discovered nearer than the 

 cuttings at the Tetbury road station, eight miles distant. The Great Oolite has now been 

 traced upwards throughout the Minchinhampton district, but there yet remains a sub- 

 division of the formation to be noticed ; this consists of sandstones, nearly worthless for 

 economic purposes, and of but little interest to the Palaeontologist; they constitute the entire 

 series of beds which underlie the limestones, and usually terminate downwards in Stones- 

 field slate, or have one or two beds which approach the slate in mineral character. These 

 sandstones must be regarded as merely continuations of the Weatherstone beds, but are nearly 

 or quite destitute of shelly detritus and crystalline structure ; for it is a curious but un- 

 doubted fact that the shelly weatherstones never have the limestones incumbent upon them. 

 All the quarrymen are aware of the fact from the experience which they have gained in the 

 numerous trials for weatherstone. At Bussage an instance may be seen of a weatherstone 

 quarry passing into a worthless sandstone on approaching the area covered by the lime- 

 stone ; occasionally, indeed, the sandstones disclose a cluster of Pholadomya3, and in the 

 vicinity of the Stonesfield slate contain some other bivalves which are never found in the 

 shelly beds. Occasionally over some small areas good serviceable quarries of weatherstone 

 are worked in situations where scarcely a single perfect shell can be procured ; there is then 

 a dense, finely comminuted, shelly detritus, and the rock abounds with calcareous spar, and 

 becomes thick bedded ; several quarries of this description have been worked in the parish 

 of Avening with good success ; in this condition the rock presents an exact counterpart to the 

 general aspect of the freestone beds in the middle portion of the Inferior Oolite in Gloucester- 

 shire, except that perhaps in the latter formation the oolitic grains are rather more abundant. 

 One of the most forcible impressions conveyed to the mind by a survey of the testacea 

 of this formation, when compared with that of the other members of the oolitic system, is 

 the great scarcity of the Cephalopoda, so few indeed are they, that the entire number procured 

 during the last twelve years may almost be counted. For this scarcity we think we can per- 

 ceive a compensation in the appearance of several genera of zoophagous gasteropods, in such 

 numbers as must effectually have checked any undue predominance which might have been 

 acquired by the phytiphagous mollusca, in the absence of the Cephalopoda. When the 

 Phasianella: and Natica3, which are now known to be zoophagous, are added to our species 

 of flesh-eating mollusca, it will at once be perceived how amply nature provided for the 

 maintenance of the balance of the testaceous animals during the deposition of the Great Oolite 

 of England. The great mass of the testacea are bivalves, and in species they exceed, by 

 about one fourth, the united number of the Gasteropoda, Cephalopoda, and Echinodermata. 



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