THE CORALLIAN ROCKS OF ENGLAND. 



291 



dated, aud split into blocks with ease. It is on the surface of such 

 blocks that the majority of the fossils are found. The Hemicidarids 

 and other urchins, for which the locality is celebrated, lie in great 

 profusion on the surface of some of the lower beds, where they are 

 protected by the intervening brash. The circumstances of the de- 

 position of these rocks are not unlike those which formed the false- 

 bedded series of the Xorth-Dorset district ; but the fossils point to 

 a later age — namely, that these Calne oolites are contemporaneous 

 and alternate with the true Coral Rag with Cidaris florigemma, 

 which they contain in abundance, associated with a tolerably rich 

 fauna, in which the absence of Corals and the abundance of Gas- 

 teropods may be noted, viz. : — 



Phasianella Bavignieri (J)' Orb.). 

 (Jhenmitzia corallina (D'Orb.). 

 Littorina pulcherrima (DoUf.). 

 Turbo faniculatns (Ph.). 

 Cerithiam lirrue forme (Bom.). 



Hambertinnni (Buv.). 



rnuricatum (Sow.). 



Trochotouia tornata (Ph.). 

 Mjtilus pectinatus (Sow.). 



angulatus (Y. §~ B.) (small). 



Lima rigida (Sow.). 



Lima sabantiquata (Bom.). 

 Pecten lens (Sow.). 



qualicosta (Et.). 



strictas (Miinst.). 



Aricala pteropernoides (Bl. <§• H.). 

 Perna mytiloides (Lam.). 

 Cidaris florigemma (Ph.). 

 Acrosalenia decorata (Haime). 

 Hemicidaris intermedia (Flcm). 

 Stomechinas gyratas (Ag.). 



"We seem to see in these false-bedded oolites of Calne the physical 

 conditions of the false-bedded series of Xorth Dorset, which, beyond 

 that area, may be traced as far as AVestbury, and even to Steeple 

 Ashton ; but the fauna is richer and very different. This is no 

 doubt due, in part, to the closer proximity of a reef. The form of 

 deposit seen in the great quarries is probably exceedingly limited ; 

 for in the direction of the false dip we immediately come to the 

 before-mentioned well, where its thickness is much less, and the 

 upper beds are becoming quite rubbly; and amongst them are found 

 the great corals of the period, which are also scattered over the fields. 

 In this latter form the Coral Rag overlies the clay near Fisher's 

 Brook. 



A third form of the deposits of this age is the exceedingly inter- 

 esting one at Hillmarton. On the south-west side of the small 

 stream that descends from the Chalk is a plateau, into which two 

 openings have been made for the extraction of road-stone. In the 

 deepest of these, which has more the appearance of a clay-pit than 

 of a quarry, are seen a series of dark-blue bands of clay, separated 

 by beds of limestone of the same colour (fig. 4). These limestones 

 are not even -surfaced, but irregular above and below : the deepest 

 appear to be the thickest and most crystalline, and are often per- 

 ceptibly formed of Thamnastrrean and Thecosmilian corals ; the 

 upper bands are thinner, lighter-coloured, and more earthy, becoming 

 near the surface almost like chalk. 



These upper bands are so uniform in substance, and so evidently 

 altered from their original state, that we must consider the lower 

 crystalline and coralline bands the normal form ; and it seems 



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