Dr. Wheelton Hind — Zones of the Carboniferous. 255 



V. — On Zonal Divisions of the Carboniferous System. 

 By Wheelton Hind, M.D., B.Sc.Lond., F.R.C.S., F.G.S. 



THE question of the zonal division of the Carboniferous system 

 has been raised during the last twelve months, and certain 

 fossils have already been mentioned as typical of a certain succession 

 in a certain district or traverse of rocks. Having studied the 

 Carboniferous system in most of the districts of Great Britain and 

 Ireland where the beds are exposed, and chiefly from a 

 palaeontological point of view, I beg to offer for discussion a few 

 of the facts of biological distribution which have come to my 

 knowledge. 



There exists, however, a great initial difficulty, one, indeed, 

 which can be gradually overcome, and this is the involved and 

 uncertain state of the nomenclature of Carboniferous Palaeontology 

 at the present time. True, that our knowledge of the Brachiopoda 

 of this period is, through the labours of Davidson, well advanced, 

 and that there is some degree of accuracy in the nomenclature of 

 this group, and its synonymy has been well worked out; but if the 

 other groups are in the almost hopeless muddle which I find to 

 be the case with the Carboniferous Lamellibranchiata, I shall be not 

 far short of the truth if I say that at the present time no reliance 

 whatever can be placed on the species and genera, so glibly 

 catalogued in the majority of the works on the Carboniferous 

 system, as being present in, or characteristic of, certain strata. 



Some time ago Mr. Morton attempted to define zones in the 

 Carboniferous Limestone beds of North Wales. He did, indeed, 

 succeed in establishing a certain definite sequence in the rocks, but 

 biologically he is able to establish no zones or horizons typified by 

 certain organisms which could be traced across country and 

 recognized as one in different localities. 



Before discussing the brief details of zonal distribution given by 

 Messrs. Garwood and Marr, 1 it will be well to ask what is meant 

 by zonal succession^ I take it, that the idea in seeking for zones 

 of rock, which can be identified by the restricted presence of certain 

 forms of life in definitely marked horizons, is to establish a 

 biological classification of strata. The presence of certain fossils 

 in any given bed is not a simple matter, and is the result of many 

 factors. 



A classification of a series of rocks by the horizontal distribution 

 of its fossils, may be always feasible locally, but such a classification 

 is of little real value unless it can be shown to be constant over 

 large areas. As a matter of fact, the distribution of marine 

 organisms is dependent to a very large extent on the depth of 

 water, and zones of life are those of isobathymetrical distribution. 

 In order that the same fossils should be found at certain horizons 

 over a large area, it would have been necessary that the sea-floor on 



1 Geol. Mag., Dec. IY, Vol. II, 1895, pp. 474, 550-2. 



