OF THE CARBONIFEROUS SERIES. 645 



the Yoredale-beds, Millstone Grit, and Gannister beds, are (as we have 

 seen) palseontologically connected with the Mountain Limestone, 

 while in composition and mineral character they are more nearly 

 related to the Upper Carboniferous beds. It was in view of their 

 mineral character exclusively that they were originally grouped with 

 the Coal-measures into an Upper Carboniferous series ; for it is only 

 recently that their palaeontological and stratigraphical relations to 

 the Middle Coal-measures have been made out. The small develop- 

 ment of coal in these earlier stages, as compared with the later, and 

 certain minor differences in the arrangement of the strata, serve to 

 distinguish the two sets of beds mineralogically. To this may be 

 added evidence of a break in the continuity of the strata at the base 

 of the Middle Coal-measures in Lancashire *, thus affording proof 

 that the change of the fauna was coincident with, and was due to, 

 changes in the physical conditions of land and water. 



It is true, however, that tripartite classifications have in several 

 instances been proposed ; but they are open to similar objections as 

 in the case of the binary divisions. Sir R. I. Murchison arranges the 

 Carboniferous series of the British Isles and Europe into three stages, 

 the lower of which only includes the Lower Limestone Shale and 

 Calciferous Sandstone, while the middle includes all the strata up to 

 the Millstone Grit ; the Lower, Middle, and Upper Coal-measures 

 are grouped in the upper division f. 



Mr. H. B. Woodward, in his ' Geology of England and Wales ' 

 (1876), adopts a binary classification, placing all the beds below the 

 Millstone Grit in the " Lower Carboniferous," and all above in the 

 " Upper Carboniferous." The objection to this arrangement is that 

 it unites beds which are palseontologically different, and separates 

 those which are palseontologically similar. 



Sir C. Lyell, in his ' Student's Manual,' has also adopted a binary 

 division, placing all the beds above the Carboniferous Limestone in 

 the upper, and those below this horizon in the lower division. 



Professor Geikie, in his edition of Jukes's ' Manual of Geology,' 

 judiciously avoids the difficulty of the subject by omitting to make 

 any classification at all ; yet, for general purposes of correspondence 

 or description, some classification appears highly desirable. 



Mr. Lebour also adopts a binary classification, placing the beds 

 below the Millstone Grit, including " the Bernician" and " Tuedian" 

 groups, in the lower division, all above this in the upper. 



Prof. E. Renevier, in his ' Tableau des Terrains sedimentaires '£, 

 gives the following classification : — 



Ages=Etages. English equivalents, 



Carbonif ere superieure : Houiller Coal-measures. 



„ moyen: Culm Millstone Grit, 



„ inferieur: Condrusien Mountain Limestone, 



„ ,, Ursien (Lower) Limestone Sbale, 



Carboniferous Slate, &c. 



* The section showing the break occurs near Bury, and is figured and de« 

 scribed by myself in the memoir on the Geology of the Country around 

 BoJton-le-Moors, p. 6 (1862). 



t ' Siluria,' 4th edit. p. 404. 



\ Lausanne. 1874. 



Q. J. G, S. No. 132. 2 1: 



