490 T. C. Cantrill — Coal-boring at Presteign, Radnorshire. 



carbonate. The purplish-red colour of this quartzite pebble is due 

 to a slight film of red iron oxide tbat coats most of the grains. 



Having these characters, the rock represented by this core agrees 

 closely with some of the Longmyndian conglomerates, rather than 

 with the softer and calcareous grits of the Upper Llandovery. The 

 large diameter of the core and the fact that all the conglomerates 

 met with in the borehole lie between the depths of 54 ft. 4 in. and 

 147 ft. 6 in. lead me to refer the specimen to some unknown position 

 between these limits. Moreover, at 180-200 feet the core-diameter 

 was only 2£ inches. The record is, however, not sufficiently detailed 

 to enable the base of the Llandovery to be located, though the 

 mention of " green-grey sandstone " in Item 16 suggests Long- 

 myndian. I conclude, therefore, that while the upper part of the 

 93 feet of conglomerates, etc., is Upper Llandovery, the lower part 

 is Longmyndian. This is not at all improbable in view of the 

 outcropping of conglomerates of this age at Pedwardine, 1 6 miles to 

 the north-east, and at Old Radnor, 2 5 miles to the south-west; and 

 it is not unlikely that the claret-coloured pebbles in the Llandovery 

 grits of the Corton Quarry were derived from the neighbouring 

 Longmyndian conglomerates. 



At 147 ft. 6 in. the boring passed abruptly into a thick series of 

 grey shales with a few thin grits and sandstones. Many of the beds 

 are described as broken and veined with spar. That these grey 

 shales are Silurian is proved by their yielding Phacops longicaudatus ? 

 (Murch.) and Monograptus cremdatus or its near ally If. vomerinus 

 at a depth of 180-200 feet. Mr. Philip Lake, to whom I am 

 indebted for an examination of the trilobite fragments, considers 

 that this species indicates a AVenlock horizon. Miss Elles thinks 

 that the graptolite shows the beds to be low in the Wenlock Shales. 

 It would seem, therefore, that the grey shales from 147^ feet down- 

 ward must be regarded as Wenlock Shales, and that the boring 

 passed into them from the Longmyndian through a fault (Fig. 2). 

 The 12 ft. limestone (Items 37-39) is probably a sporadic band and 

 can hardly be the Woolhope Limestone, as it is underlain, not by 

 the Upper Llandovery Sandstone, but by 535 feet of what are 

 presumably more Wenlock Shales. 



On this hypothesis a section through the borehole might be 

 represented diagrammatically as in Fig. 2. 



It is improbable that the dip of 55° seen in the exposures of the 

 Upper Llandovery Sandstone close to the borehole prevails under- 

 ground. The dip as seen in the cores below 147£feet seems to vary 

 from 20° to 30°. From these rather meagre data the minimum 

 displacement of the fault may be estimated at 888^ — 29| = 

 858f feet, a throw that would carry down the Woolhope Limestone 

 to some position below the bottom of the borehole. And as the 

 Woolhope Limestone, Upper Llandovery, and supposed Longmyndian 

 in the boring overlie Wenlock Shales, the fault must be an over- 

 thrust from the south. The thrust-plane, which would reach the 



1 A. H. Cox, " The Pedwardine Inlier " : Quart. Journ. Geol. Soc, 

 vol. lxviii, 1912, p. 364. 



2 C. Callaway, Quart. Journ. Geol. Soc, vol. lvi, p. 511, 1900. 



