﻿Vol. 66.~] LIMESTONE SOUTH OF THE CKA.VEN FAULT. 575 



Laithe Quarry : several species of Zaphrentis are common in the 

 same quarry ; the Cyathophyllum figured is also very plentiful, 

 but I have rarely found it elsewhere. (PI. XL, fig. 6.) 



Caninia hettonensis, which occurs at Owslin Barn, and at Hetton 

 and elsewhere, is very common in the former very small cutting. 

 Two bands of muddy shale are, in places, crowded with specimens. 



Cyathophyllum regium is common at Dibble's Bridge, but is 

 rarely found elsewhere in the whole district described. 



The most remarkable example of this localized abundance is that 

 of the corals from the Bylstone Railway Quarry, mentioned in the 

 description of that quarry and in the notes on the corals. 



Small forms of Caninia (as, for example, cornucopias), Zaphrentis, 

 and Cyathaxonia seem to be almost wanting in the white limestone 

 of Elbolton and Swinden district ; on the other hand, Lithostrotion 

 and larger forms of Caninia are quite common. 



The genus Syringopora occurs in countless masses in the Hetton, 

 Eshton, and Bell Busk districts ; it seems to be comparatively rare 

 in the limestone of the Knolls. 



With respect to such cases as the Bylstone ' colonies,' it may be 

 that if other exposures could be obtained on precisely the same 

 horizon, we should get at least most of the species that occur 

 there in such numbers. Mr. Carruthers wrote (Geol. Mag. dec. 5, 

 vol. v (1908) p. 170) :— 



' . . . In Scotland, certainly, small rugose corals of this type are noticeably 

 local in their distribution. In a bed whose position is accurately known over 

 a wide area, they appear and disappear in a remarkable manner, as if they 

 were very sensitive to conditions of deposit and food-supply.' 



For a further admirable discussion of this subject, see a more 

 recent paper by Mr. Carruthers. 1 



Another feature of importance in the distribution of the corals 

 is the association of species and varieties which are, in some other 

 provinces, characteristic of different horizons- 



Caninia gigantea evidently occurs at a higiifr horizon here ; at 

 Crag Laithe and at Swinden Gill Head it is found plentifully in beds 

 which are only separated by some 40 to 60 feet or so from calcareous 

 shales containing Cyathaxonia. 



The coral fauna of Crag Laithe Quarry is somewhat mixed, in- 

 cluding forms which are suggestive of D 3 or even P, as well as 

 forms like Carcinophyllum and Zaphrentis delanouei which suggest 

 D t or D 2 . The brachiopod fauna is suggestive of a high horizon, 

 probably D 3 . It would seem that the horizons J) v D 2 , D 3 are not 

 represented by a great thickness of beds here. 



In the neighbouring region of Rain Hall the d mutation of 

 Caninia cornucopias is found in the same beds as the true species. 



The association of Cyathaxonia comu with G. rushiana has been 

 already mentioned as being of some interest. 



1 Geol. Mag. dec. 5, vol. vii (1910) p. 171 , 



