THE COPvALLIAN ROCKS OF ENGLAND. 295 



This quarry is also valuable in another respect — viz. that though 

 we see here the whole section, the marls of Calne, which lie between 

 the Coral Hag and Lower Calcareous Grit, are absent ; and. though 

 the physical and petrological connexion is indicated by the mixture 

 of the marl with oolite in the pit at Green's Cleeve, yet here their 

 place is entirely taken by oolites, which we may thus compare to the 

 " Coralline Oolite " of Yorkshire, or the false-bedded series of the 

 south. We begin, too, to learn how characteristic Naticce are, in 

 this district, of the lowest fossiliferous beds. 



4. WOOTTON BASSETT TO HlGHWORTH". 



The rubbly Coral Bag which we saw occupying the whole Coral- 

 lian area at Lyneham Hillocks, towards Wootton Bassett, continues 

 to dominate in the neighbourhood of and beyond that town to the 

 west, so that for some considerable extent of country hereabouts the 

 name would be appropriate for all that is seen between the Oxford 

 and Kimmeridge Clays. Its thickness at Wootton Bassett is about 

 25 feet ; and it is in the form of a brash and rubbly coarse-grained 

 oolite in which Cidaris florigemma is abundant. At Banner's 

 Ash, a locality quoted by Smith, it is in the form of a true reef, with 

 massive Thamnastraean corals in full development, and with an abun- 

 dant fauna, including Nerita Ouerrei, and excluding Phasianella 

 striata, which is elsewhere so common. Traces of the existence of 

 some gritty beds below may be noted in brooks and similar expo- 

 sures ; but they make no show upon the surface. 



The maximum development hereabouts seems to take place in the 

 neighbourhood of Burton, where the change of strike from JS T .E. 

 to more nearly E. occurs. The miuor exposures are numerous; and 

 whether of much thickness or not, the Corallian rocks are of con- 

 siderable surface-importance. The chief exhibition of them is seen 

 in a fine old quarry about f of a mile east of the village. 



Section at Purton. 



ft. in. 



1. Rubbly coral bed, showing several lenticular masses 



of Thamnastrsean corals, of only limited extent, 

 from a few inches to 1 foot in thickness, the re- 

 mainder made up of broken pieces and Theco- 

 smilice, as if washed about on the spot. It 

 contains the usual coral-bed fossils. Thickness... 7 6 



2. Blue-hearted strong limestones in courses, forming 



flags, not oolitic, but formed of shell-fragments ; 

 the division between the layers often consists of 

 more shelly and less compact limestone-rubble. 

 The stone is used for building and paving, and 

 is not at all false-bedded. The fossils are all 

 broken ; but among them may be recognized Litto- 

 rina muricafa, Perna mytiloides, Pecten vimineus, 

 Lima rudis, Lima rigida, Avicula ovalis, Cidaris 

 florigemma, and abundance of small oysters. 

 Thickness 10 



