Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/759

Rh OF THE CARBONIFEROUS SERIES. 649 This classification rather closely approaches the one here suggested. In the 3rd edition of the ' Coal-fields of Great Britain,' having recognized, though not so fully as at present, the palaeontological connexion between the Gannister Beds (Stage E) and the Mountain Limestone, I placed all the beds from this formation downwards inclusive in the "Lower Carboniferous" division. Though this arrangement is, from my point of view, preferable to that which places all the beds above the Limestone in the Upper Carboniferous division, it is open to the objection of not sufficiently recognizing petrological characters and affinities. The conflicting views amongst authors above noticed is to be attributed to the want of some clear principle upon which to deter- mine the relationshijDS of the various members of the Carboniferous series to each other. The palaeontological differences between the Gannister Beds and the Coal-measures seem to offer a good basis for drawing a divisional line at this horizon ; while the petrological differences between the Carboniferous Limestone and the succeeding stages, together with the great destruction of coralline, crinoidal, and molluscan life at the close of the former stage, afford sufficient grounds for drawing another line of division at this lower horizon, — thus con- stituting a middle Carboniferous group, the beds of which are closely related in mineral and palaeontological characters. (e) Proposed Classification. In order, therefore, to give the affinities and differences in the Carboniferous beds due recognition, it seems desirable to adopt a threefold arrangement, constituting a middle group differing from the lower in mineral characters, and from the upper in the characters of the prevalent molluscan fauna ; and with this object the arrangement shown in Table I. p. 640, seems to me the most natural that can be adopted. In speaking of the main divisions as " essentially marine," " essentially lacustrine," &c, I wish those terms to be understood as representing the prevalent conditions, which admit of exceptions, as in the case of the Lower Carboniferous group, which, though essentially marine, contains in Scotland marginal representatives of the period which are estuarine and lacustrine in character. (/) Summary of Conclusions. From the above considerations it is to be inferred that the Gan- nister Beds (Stage E) should be dissociated from the main mass of the coal-measures above, and grouped with the formations below : — First. Because Stage E is essentially of marine origin, while Stages F and G are essentially estuarine and lacustrine. (See Table III.). Secondly. Because the few marine species found in Stages F and G are for the most part specifically different from those in Stage E. (See Table IV.) Thirdly. Because of local breaks in stratification between Stages E and F, concurrent with the palaaontological break*.
 * An illustration of Professor Ramsay's views, as expressed in his Presidential