538 E. Wethered — Organisms in Carboniferous Limestone. 



remains of Ostracoda, among which Professor Jones has distinguished 

 Leperditia and Cytherella, but as we have not been able to separate 

 any from the matrix, the species have not been determined. In 

 addition to Ostracoda, the rock contains remains of Foraminifera 

 badly preserved, also occasional Polyzoa, and the spines (and possible 

 shell fragments) of Productus. 



General View of The Upper Limestones. 



The beds of the Upper Limestones indicate a return of conditions 

 not unlike those which existed at the time of the deposition of the 

 Lower Limestone Shales. At the period of the latter, the Carbon- 

 iferous Limestone was about to commence ; at the period of the 

 former, it was near to its close, and the great Coal epoch was 

 soon to dawn. From what I have said respecting the changes which 

 the beds of stage B, or the Carboniferous Limestone proper, have 

 undergone, it is difficult to say what fossils they contained or what 

 organisms contributed to the formation of the limestone ; but in the 

 Upper Limestones we get a return of life similar to that which con- 

 tributed so largely to the Lower Limestones. I therefore contend 

 that I am justified in forming a separate division of the Upper Lime- 

 stones. If I am not, then there is no justification for making a 

 separate division of the Lower Limestone Shales. 



Chemistry. 



As in the case of limestones generally, the Lower and Upper series 

 have been consolidated by the deposition of calcite in the vacant 

 spaces between the organisms and other calcareous fragments. With 

 regard to the Carboniferous Limestone, that, too, undoubtedly 

 originated from calcareous organisms, but a subsequent change 

 occurred which replaced the original structure with magnesia and 

 possibly some calcite. I am not aware that dolomitization in the 

 Carboniferous rocks of the Forest of Dean has before been noticed, 

 but it has in other localities. Mr. Sorby, F.E.S., states 1 that "in 

 Derbyshire and elsewhere some of the beds are almost pure dolomite. 

 As far as can be judged from their structure, they may have been 

 normal limestones completely changed after deposition, and cer- 

 tainly do enclose dolomitized shells, Corals, and Encrinites." The 

 late Professor Harkness called attention to the same thing in a 

 paper 2 "On the Jointing in the Carboniferous and Devonian Eocks 

 in the district around Cork and on the Dolomite of the same district." 

 The limestone referred to by Professor Harkness has undergone 

 considerable jointing, which he considered to be a factor in the pro- 

 cess by which those particular beds became dolomitized. He says : 3 

 "The whole aspect of the Carboniferous dolomites of Cork and 

 Kilkenny leads to the inference that certain changes have been 

 effected on previously existing masses of carbonate of lime ; and 

 the general parallelism which occurs between these dolomites and 



1 Quart. Journ. Geol. Soc. Proc. 1879, vol. xxxv. p. 87. 



2 Quart. Journ. Geol. Soc. vol. xv. p. 86. 



3 Quart. Journ. Geol. Soc. vol. xv. p. 103. 



