540 Aubrey Strahan — Mocks beneath the Coal-measures 



magnesium sulphate, we can readily understand. That dolomite 

 can be produced by the decomposition of magnesian chloride in the 

 presence of Iceland spar has been proved by Mr. Sorby, F.R.S. 1 



EXPLANATION OF PLATE XIV. 



Fig. 1. Crinoidal Limestone, Lower Limestone Shales. 

 ,, 2. Apparent pentagonal stem joint of a Crinoid, from the same hed as Fig. 1. 

 ,, 3. Lower Limestone Shales, contains remains of Ostracoda, occasional Polyzoa, &c. 

 ,, 4. Lower Limestone Shales, chiefly made up of the remains of Ostracoda. 



The infilling calcite in the spaces between the organisms is well illustrated 



in this specimen. 

 ,, 5. Lower Limestone Shales, chiefly made up of minute calcareous fragments 



and concretions. 

 ,, 6. Mitcheldeama Nicholsoni. 



PLATE XV. 



Fig. 7. Dolomitized Carboniferous Limestone. 

 ,, 8. Dolomitized Carboniferous Limestone, the outlines of previous structure 



remaining. 

 ,, 9. " Crease Limestone," base of Upper Limestone Series. 

 ,, 10. "Whitehead Limestone," Upper Limestone Series, showing remains of 



Ostracoda and Polyzoa. 

 ,, 11. Oolitic Limestone, Upper Limestone Series. 

 ,, 12. "Whitehead Limestone, another bed, showing remains of Ostracoda, spines of 



Productus, etc. 



IT. — On the Rocks surrounding the Warwickshire Coal-field, 

 and on the Base of the Coal-measures. 2 



By Aubrey Strahan, M.A., F.G.S., 

 H. M. Geological Survey. 



With Appendix I. on the Igneous Bocks of the Neighbourhood, by Frank Butley, 

 F.G.S. Appendix II. on the JSew Species Olenus Nuneatonemis and Obolella 

 granulata, by G. Sharman. 



(Communicated by permission of the Director-General.) 



IN a paper read before the Birmingham Philosophical Society in 

 ]882, it was announced by Professor Lap worth that the dis- 

 covery of fossils in some shales underlying the productive Coal- 

 measures of Warwickshire, and coloured on the Geological Survey 

 Map as Coal-measures, proved that these shales must be of Cambrian 

 age (Lower Silurian of the Geological Survey). 3 As the true age 

 of these shales had for many years been a debateable question, 

 Professor Lapworth's discovery was of considerable interest, and 

 has led to an important alteration being made in the map, the sup- 

 posed Lower Coal-measures and Millstone Grit having both been 

 now relegated to the Lower Silurian (Lingula Flags). It may 

 be of interest, before entering on the description of these beds, to 

 trace shortly the history of the error in their classification. 



The first notice referring to the older rocks of Warwickshire that 



1 Quart. Journ. Geol. Soc. Proc. 1879, vol. xxxv. p. 73. 



2 Bead before Section C. (Geology), British Association, Birmingham, Sept. 2, 18S6. 



3 The nomenclature of the Geological Survey, according to which the Lingula 

 Flags are included in the Lower Silurian, will be used throughout this paper. 



