Reports and PvoceeiU)i(js — Geological Socktij of London. 4-> 



quantities of carbonates. In a second example, felspar fragments- 

 appear as a meshwork of rods which extinguish simultaneously,, 

 and are embedded in an isotropic groundmass crowded with globu- 

 lites and little rods. A faint streakiness, which cannot be fluxion- 

 structure, passes through the matrix of the rock and the meshwork 

 of the felspar fragments without deflection. Analyses of the rocks 

 and diagrams constructed from their molecular ratios correspond 

 closely with those of soda-rhyolite and potash-rhyolite respectively. 



III.— Dec. 5, 1900.— J. J. H. Teall, Esq., M.A., F.R.S., President, 

 in the Chair. The following communications were read : — 



1. " On the Corallian Rocks of St. Ives (Hunts) and Elsworth." 

 By C. B. Wedd, Esq., B.A., F.G.S. (Communicated by permission 

 of the Director-General of the Geological Survey.) 



Starting 2| miles south-west of Elsworth, the author traces the 

 Elsworth Rock at intervals through Croxton, Yelling, Papworth 

 Everard, etc., to Elsworth, and thence towards Fen Drayton and 

 near Swavesey. The Oxford Clay is found to the west of it, and the 

 Ampthill Clay to the east. Frequent fossil lists are given, and 

 the character of the rock is described at the different exposures. 

 Again, from Haughton Hall, west of St. Ives, the ' St. Ives Rock ' 

 is traced through that town and towards Holywell. The actual 

 connection with the Elsworth Rock cannot be seen owing to an area 

 of fen. But that the two rocks are identical the author considers 

 is proved by the consistency of the two rocks, the absence of any 

 other rock-bed, the dip of the strata, and the presence of Ampthill 

 Clay above. The Corallian strata of the area appear to have been 

 deposited more slowly than the Oxfordian strata. Of the two 

 zonal ammonites of the Corallian, the dominant form in the Elsworth 

 Rock and in the stone-bands of the Ampthill Clay is of the i^licatilis 

 and not \\\q i^erarmatus t3'pe. 



2. "The Unconformity of the Upper (red) Coal-measures to the 

 Middle (grey) Coal-measures of the Shropshire Coalfields, and its 

 bearing upon the Extension of the latter under the Triassic Rocks." 

 By William James Clarke, Esq. (Communicated by W. Shone, 

 Esq., F.G.S.) 



The Upper Red Measures have a much greater extension in the 

 Shropshire Coalfields than the productive measures below. In the 

 Shrewsbury field they are the only Carboniferous rocks present, and 

 rest on pre-Carboniferous rocks. 



When the sections of collieries at and near Madeley are plotted 

 on the assumption that the base of the Upper Carboniferous rocks 

 is horizontal, the Lower Measures are found to be bent into a 

 syncline rising sharply to the north-north-west and more gently to 

 the south-south-east. A second syncline, broader and deeper, 

 extends from Stirchly towards Hadley, but the westerly rise is often 

 hidden by the boundary-fault of the coalfield. This phenomenon is 

 known locally as the ' Symon Fault ' ; and instead of taking Scott's 

 view that it represents a hollow denuded in the Lower Coal-measures, 

 the author considers it due to folding: before late Carboniferous times. 



