﻿Vol. 64.] CAEBONIFEEOUS LIMESTOISTE OF THE MIDLAND AEEA. 37 



described briefly, and the changes of lifchological facies in that 

 subzone discussed. The Gi/atha.voma-s\ihzone is then traced, in its 

 varying development, throughout certain parts of the area, and the 

 relation of this highest subdivision of the Avonian to the overlying 

 Pendleside Shales is exemplified. A local unconformity between 

 the Carboniferous Limestone and the Pendleside Shales is described 

 in a separate section. After a comparison of the succession in the 

 Midlands with that in other areas, and a summary of conclusions, 

 the paper concludes with the description of certain corals and 

 brachiopods. 



II. The Typical Sequence of the Midland Aeea. 



Section along the course of the Midland Railway between 

 Longstone and Buxton. 



This is by far the most extensive sequence exposed in the area. 

 The cuttings on the railway, together with numerous quarries and 

 •other exposures adjoining the line, afford a nearly-continuous section, 

 which extends over more than 8 miles, in a roughly east-and-west 

 direction, through the dales. The succession is described and illus- 

 trated in the Geological-Survey Memoir,^ pp. 18-21, fig. 2 & pi. ii. 



At the eastern end of the section a cutting west of Longstone 

 Station shows the uppermost beds of the Carboniferous Limestone, 

 dipping eastwards to pass conformably under the Pendleside Shales. 

 Westwards from this point, as far as Pig-Tor Tunnel, a distance of 

 about 6| miles, successively lower parts of the Carboniferous Lime- 

 stone are seen. Throughout this distance the beds have a very 

 gentle easterly dip, interrupted here and there by slight undulations. 

 The base of the Carboniferous Limestone is not seen, for at Pig-Tor 

 Tunnel the anticlinal axis is reached, and the westerly dip which 

 there sets in persists to the end of the section. At the western 

 end, on the railway near Buxton, a considerable thickness of the 

 upper beds of the Carboniferous Limestone has been faulted out, 

 and the junction of the lower beds with the Pendleside Shales is 

 obscured. 



In a section so extensive as this one, and with slightly-inclined 

 and undulating beds, estimations of vertical thickness are necessarily 

 open to considerable error. In the accompanying table (p. 38) my 

 own reading of the sequence is given, together with that of the Geo- 

 logical-Survey Memoir. The difference between the two estimates 

 of total thickness is comparatively small, and lies within the probable 

 error of determination. With reference to these two estimates, 

 we may conclude that the total thickness of Carboniferous Limestone 

 exposed in this section, exclusive of the intercalated toadstones, 

 approximates to 1500 feet. 



In one or two important points, my own reading of the section 

 differs from that which is set forth in the Geological-Survey Memoir. 



^ ' Geology of the Carboniferous Limestone, &c., of North Derbyshire * 

 2nd ed. 1887. 



