104 



L. M. Parsons — 



Dolomitization in the Carboniferous Limestone of the 



Midlands. 



By L. M. Parsons, M.Sc, D.I.C, F.G.S. 

 (WITH PLATE VI.) 

 {Concluded from p. 63.) 



IV. The Dj Dolomitic Limestones of Gratton and Long Dale. 



The middle portion of tKe Dj beds seen in the Gratton Dale section 

 consists of about 630 feet of dark dolomitic limestones, which 

 appear to be confined to a definite horizon in the sequence. The 

 impression one at first receives is that here are definitely bedded 

 dolomites probably of contemporaneous origin, and this material 

 has already been referred to as a thick bed of dolomite.^ Working 



UNALTERED LlMBSTON£ 



OOLOMITIC LIMESTONE 



, OyVS MILE 



3= 



Fig. 3. — Map illustrating dolomitization in Gratton Dale and Long Dale. 



northwards down the dale, i.e. ascending the sequence, one finds 

 that the vertical passage from normal limestone into dolomitic 

 material above is everywhere obscured. Similarly the upper limit 

 of the dolomitized beds is covered, so that it is impossible to say 

 whether the metasomatism abruptly ceases with a certain bed or 

 dies out gradually in th e higher strata. In the affected part of the 

 sequence the dolomitization appears persistent in Gratton Dale, 

 and at a few places only have I found lateral transitions, one or two 

 examples on either side of the dale. The most marked transition is 

 on the western side, towards the upper part of the altered material. 

 Here light-coloured limestones are seen to pass laterally within 

 a few yards into darker dolomitic material, with which it contrasts. 

 Careful examination shows that these limestones on both sides 



^ Dr. H. H. Bemrose, Proc. Geol. Assoc, vol. xxvi, 1915. 



