166 David Woolacott — Borings at . 



carefully searched yields a very scanty and dwarfed fauna, consisting 

 of Bahevellia antiqua, Munst.,i?. ceratophaga, Schl., Schizodus truncatus, 

 King, Pleurophorus costatus, Brown, Astarte vallisneriana, King, and 

 Spirorbis permianus, King. The bed marked " g " in the Sheraton 

 boring with Bahevellia ceratophaga, small serpulids, and ostracod 

 valves, is the exact equivalent of these beds. The reef-like nature of 

 the Shell or Fossiliferous Limestone thus receives further confirmation 

 from these borings. 



The sections of the Middle Limestone given in these boreholes are 

 therefore of much interest as they add considerably to our knowledge 

 of the little-known western equivalents of the Reef. In the northern 

 part of the county the remnant of them occurs as a bedded f ossiliferous 

 maguesian limestone, the main mass having been everywhere 

 denuded, but in the south they are found as a series of cellular 

 segregated rocks and granular, oolitic, and bedded dolomites over 

 200 feet thick. The segregated part of the former rocks are nearly 

 pure calcium carbonate with powdery dolomitic infilling in the 

 cavities, while the latter beds are almost pure dolomites. 1 In both 

 borings thick beds of dolomitic oolite occurred. Such beds are of 

 much more frequent occurrence in the Magnesian Limestone than is 

 generally thought to be the case. 



These segregated, oolitic, and granular dolomites are the in-shore 

 equivalents of the Bryozoa Beef. To the east the Beef is replaced 

 by the off-shore beds consisting of segregated and yellow bedded 

 rocks, from which no fossils have yet been recorded, and which are 

 often more pseudo-brecciated and brecciated than the rocks on the 

 west. The Middle Magnesian Limestone thus presents two distinct 

 types of bedded rocks with the shell-bank of the Bryozoa Beef 

 lying between. 



The top of the Lower Limestone is fairly well marked in each 

 borehole by the merging of the Middle beds into a hard dense yellow 

 dolomite with carbonaceous partings. The bedded series beneath 

 consists of 280 feet of yellow and brown dolomitic and grey 

 calcareous limestone. These at one or two horizons alternate in 

 irregular bands, but beds over 100 feet thick of both types occur. 

 The grey calcareous rocks are among the purest of the whole of the 

 Magnesian Limestone series, containing over 98 per cent of calcium 

 carbonate, and are very similar in composition and appearance to 

 Carboniferous Limestone. They are distinctly hard and solid, but in 

 places have suffered a process of brecciation, generally apparently 

 more or less contemporaneous with the deposition of the beds. Some 

 of the more pronounced brecciation in these beds has, however, been 



1 A. D. N. Bain, B.Sc, has analysed these rocks and supplied me with the 

 following figures :— 



Granular Dolomite. Oolitic Dolomite. 



Dolomite . . .62-38 Dolomite . . .82-47 



Calcite . . .30-10 Calcite . . .17-46 



Ferric oxide . . 3-88 Ferric oxide. . . -4 



Insoluble residue . 3-46 



99-82 



100-33 



