F. Ridley — Igneous Rocks of the Warwickshire Coal-field. 557 



enormous denudation in pre-Carboniferous times, so great indeed as 

 to remove the whole of the series, consisting in the aggregate of 

 several thousand feet of rock, from parts of Leicestershire. And it 

 is probable that in the period of submergence that succeeded this 

 continental epoch most of even the higher parts of the old land- 

 surface in this neighbourhood were overspread by the latest Coal- 

 rneasure sediments. But, however this may have been, the Carboni- 

 ferous rocks were swept bodily off large areas in the Midland Counties 

 in the long period of denudation which preceded the Trias. There 

 are therefore two questions to be taken into consideration, in specu- 

 lating on the possible presence of Coal-measures under the Trias at 

 any point in the Midland Counties : firstly, whether the Coal-measures 

 ever existed at that point ; secondly, whether, having existed, they 

 were subsequently removed by pre-Triassic denudation. It is scarcely 

 possible to attach too much importance to the study of the great 

 unconformity at the base of the Trias. In the present instance 

 it seems certain, that though the Coal-measures may have been 

 deposited in a continuous sheet between the Leicester and Warwick 

 Coal-fields, they were certainly swept clean off, as far north as 

 Market Bosworth and perhaps further, before the Waterstones and 

 Marls were deposited. 



Appendix I. 



III. — The Igneous Rocks, etc., of the Neighbourhood of the 

 Warwickshire Coal-field. 



By Frank Eutley, F.G.S., etc. 



THESE rocks may be classed into five or six more or less 

 distinct groups. 

 I. Syenitic Bocks (Croft Series). 



ii. Andesite and Andesitic Tuffs (Caldecote Series). 



in. Hartshill Quartzite with Breccia at its base. 



iv. Diorites. 



v. Andesites or Diorites containing Augite. 



vi. Basalts or Diorites containing Olivine. 



The three last groups appear to graduate into one another, and 

 seem to correspond with similar rocks described by Mr. Allport. 1 

 Many of the specimens examined are in a more or less advanced 

 stage of decomposition, calcite, serpentine, pyrites, etc., being very 

 commonly present. 



The best example of diorite in the series is that from the Oldbury 

 Beservoir. These rocks are of special petrographical interest since 

 so few diorites have been found in England. The mineral constitu- 

 tion of some of these rocks is such that they are also interesting from 

 the transitional characters which they present between diorite, basalt 

 and andesite or diabase. The pseudomorphs after olivine met with 

 in the sections of rock here described might rather, as a rule, be 

 called metasomata, since well-developed forms of the original crystals 



1 On the Diorites of the "Warwickshire Coal-field, Q.J.G.S. vol. xxxv. p. 637. 



