536 E. Wethered — Organisms in Carboniferous Limestone. 



would refer this organism to the Hydractinidae, and as allied to the 

 Stromatoporoids. Professor Nicholson is himself struck with the 

 similarity of the structure to certain Stromatoporoids, but remarks that 

 he is not aware of any which have so minute a canal system of precisely 

 the same nature ; and that if it be referable to the Stromatoporoids, it 

 would probably require to be placed in a new genus. Of course I 

 am aware that Stromatoporoids have not before been noticed in 

 Carboniferous rocks, but that is no reason why they should not occur. 



In referring Mitcheldeania Nicholsoni to the Stromatoporoids, I do 

 not wish to ignore certain features which this fossil possesses in com- 

 mon with some other Hydrozoa. Professor Nicholson called my at- 

 tention to Parheria, Carp., which no doubt shows structure which is 

 also seen in M. Nicholsoni, but in the former there is a nucleus con- 

 stituted of chambers which are laid end to end in a reticulate direc- 

 tion, and separated by septa. I have not detected a nucleus of this 

 nature in M. Nicholsoni. 



Another organism which especially struck Dr. Hinde as similar to 

 my new genus is Girvanella problematica, Nich. and Ether., jun. 

 Professor Nicholson has kindly sent me rock specimens containing 

 that fossil, from which I have been enabled to get some good sec- 

 tions. As regards mode of occurrence, there is a great resemblance, 

 and also in the concentric lamination, but the minute structure is 

 quite different. 



The Carboniferous Limestone — or Stage B of Prof. Hull — con- 

 stitutes the middle division of the limestone series in the Forest of 

 Dean. Commencing with the lowest beds, I have worked upwards, 

 and in all that I have examined, the slides exhibit the same structure, 

 namely, a rock made up apparently of very small calcareous granules 

 (PI. XV. Fig. 7). It is not, however, so formed ; the key to the 

 problem is PL XV. Fig. 8, in which we see the outlines of a previous 

 structure, the whole having undergone complete change and been 

 replaced by crystalline material. The granular appearance is due 

 to the small crystals and possibly large ones which have cracked or 

 split up into fragments. As to what the replacing mineral is, the 

 following chemical analysis will enable us to judge. The sample 

 was taken from the centre of the formation, and though one analysis 

 cannot be said to prove the composition of the whole 360 feet of 

 strata, yet I believe it to be typical of at least a large portion. 



In making the analysis I was assisted by Mr. W. E. Wiltshire, 

 F.C.S. As it is important, I will state it in two forms : 



I. 



Moisture 



•02 



II. 

 Moisture 



•02 



Organic matter 



6-17 



Organic matter ... 



6-17 



Carbonic acid 



... 44-01 



Insoluble Eesidue 



1-06 



Insoluble Eesidue 



1-06 



Carbonate of Iron 



1-01 



Soluble Silica 



•10 



Soluble Silica 



•10 



Ferrous Oxide 



•63 



Carbonate of Lime 



54-00 



Lime 



... 30-24 



Carbonate of Magnesia 



37-19 



Magnesia 



... 17-50 



Carbonate of Soda with trace of 





Soda 



•25 



chlorine 



•43 



99-98 



99-98 



