542 Aubrey Strahan — Hocks beneath the Coal-measures 



had figured and described a section near Dudley, in wbicb tbe Coal- 

 measures were seen resting on Silurian sbale, botb being nearly 

 horizontal, but tbe unconformity being shown by the fact of the 

 Coal-measures abutting against a small cliff of Silurian shale at one 

 part of the section. " From this very instructive instance we learn 

 generally how, with perfect, apparent local conformability, there may 

 be still on the large scale a very great amount of unconformability 

 between two formations." From these statements it is quite clear 

 that Prof. Jukes had fully grasped the true relation borne by the 

 Warwickshire quartzite and shales to the overlying Coal-measures. 



In 1879, the results of a microscopic examination of the intrusive 

 Diorites were described by Mr. Allport, 1 who accepted the conclusion 

 of the Carboniferous age of the rocks, and it was not until the year 

 1882 that the discovery of fossils in the shales by Prof. Lapworth 2 

 finally disposed of the possibility of the beds being of Carboniferous 

 age, and established the correctness of the earlier view that the 

 quartzites with the overlying sbales were of Silurian age. This 

 being the case, it was evident that the base of the Coal-measures 

 had yet to be found, and traced upon the map, and for the purpose 

 of doing this I received instructions to proceed to the district in the 

 spring of this year. 



This task was rendered far easier than it would otherwise have 

 been by Professor Lapworth's kindness in placing freely before me 

 the results of his own observations on the Silurian rocks, and on 

 their relations to a still older volcanic series beneath, one of the 

 most valuable of these results being his discovery of fossils at 

 different horizons, ranging from near the top to near the bottom of 

 the shales. For the resemblance of the Silurian shales, and espe- 

 cially of some soft nearly black bands, to Coal-measures is so 

 striking, that in the absence of such fossil evidence the difficulty of 

 separating them would have been greatly increased. Not only are 

 the Silurian shales entirely uncleaved, and, except in the immediate 

 neighbourhood of the intrusive igneous rocks, very little altered, 

 but their dip agrees very closely both in amount and direction with 

 that of the Coal-measures, especially in the southern part of the 

 district. The clue once provided, however, it became easy to see 



(1) that the conformability of the shales with the Coal-measures is 

 apparent only, there being in reality such evidences of discordance 

 as might be expected between rocks so very different in age ; 



(2) that the Coal-measures are based by an impersistent bed of 

 sandstone containing pebbles of quartzite and of the local rocks, 

 bearing evidence (as in South Staffordshire) of having been deposited 

 in the hollows of a floor of gently inclined Silurian strata ; while 



(3) it became clear that the intrusive igneous rocks are entirely of 



1 On the Diorites of the "Warwickshire Coal-field, Quart. Journ. Geol. Soc. vol. 

 xxxv. p. 637, 1S79. 



2 On the Discovery of Cambrian Kocks in the Neighbourhood of Birmingham, 

 Geol. Mag. New Series, Dec. II. Vol. IX. p. 56'6, 1882 (reprinted from the 

 Proc Birmingham Phil. Soc. vol. iii. p. 234). See also Geol. Mag. New Series, 

 Dec. III. Vol. III. p. 319, 1886. 



