and its Bearing on the Coral Reef Problem. 197 



rock series to tlie close association of dolomites with rocks show- 

 ing oolitic structure. While some oolites have been claimed 

 to be of seolian origin most examples are clearly of very shallow 

 marine origin and by many geologists are regarded as having 

 been formed between high and low tide levels. From these 

 writings the following remarks are taken : 



" The* dolomitized rocks (Lower Syringothyris Zone C,) 

 clearly were originally crinoidal and foraminiferal limestones 

 As regards the conditions of formation of these dolo- 

 mites, the facts appear to be in conformity with the now 



generally accepted view that they originated by the 



practically contemporaneous alteration of limestone under shal- 

 low water conditions. It is a well established fact that shal- 

 lowing of the water of the Carboniferous Limestone Sea took 

 place throughout the main part of the Southwestern Province 

 in Middle Avonian times ; and the occurrence of these dolo- 

 mites on the same general horizon as the shallow water beds 

 elsewhere, is evidence that the shallowing extended to the 

 Mendip area." Dixon and Vaughan,f referring to the charac- 

 ters of the S 2 or "modioliC phase of the Carboniferous Lime- 

 stone of the Gower Peninsula in South Wales, remark : — 



"Contemporaneous erosion is evidenced in some of the oolites 

 by irregular fragments, also of oolite, measuring up to 2 feet 

 in length ; in such beds, dolomite, if present, is more abundant 

 in the matrix than in the fragments." 



Sibly4 referring to the Carboniferous Limestone of the 

 West of England, states — "In the Bristol area shallow water 

 prevailed during the greater part of Syringothyris time, as 

 evidenced by the extensive development of pure oolite, shales 

 and dolomites in the Syringothyris zone In the Men- 

 dip area the Syringothyris zone, which is considerably thicker 

 than in the equivalent part of the Bristol zone, consists entirely 

 of fossiliferous limestone. The Weston-Super-Mare district 

 between the Bristol and Mendip areas exhibits an intermediate 

 t}'pe of development of the Syringothyris zone. The lowest 

 zone is appreciably dolomitized, and is succeeded by a thick 

 band of pure oolite " 



Dixon, § describing the dolomitization of the Carboniferous 

 Limestone of the Gower Peninsula, remarks as follows : — 



"Laminosa dolomites occur in the Bristol district, in Gower, 

 and West of Tenby, and throughout this long extent dolomites 

 replace a variety of limestones Further South, how- 

 ever, in the Mendips and South of Tenby, limestones on the 



* Eeynolds and Vaughan, Q. J. G. S., lxvii, 348-349, 1911. 

 + Dixon and Vaughan, Q. J. G. S., lxvii, 488, 1911. 

 t Sibly, Q. J. G. S., lxii, 356, 1906. 



§ Dixon, Swansea, Memoir, No. 247, Geol. Sur. of Gt. Britain, 1907, pp. 

 15-17. 



