Yol. 55.] STRUCTURE OF THE SOUTHERN MALYERNS, 167 



semilyrate form of the escarpment. The actual junction of the 

 Llandovery Beds with the older series is nowhere shown, but its 

 position can, in most places, be fixed within narrow limits. 



The beds immediately underlying the Llandovery Sandstone and 

 Conglomerate along the whole length of the escarpment are the 

 Grey Shales, or possibly, south of Martins, igneous rocks associated 

 with them. Only in Castle Coppice is this natural junction 

 replaced by a faulted one ; a block of Llandovery Sandstone is 

 here brought down agaiast the basal Llandovery Beds of the 

 escarpment. 



It is important to note that the strike of the Grey Shales is 

 generally about parallel to that of the May Hill Beds above, the 

 former evidently turning round through all the marked curves 

 shown by the latter. In the absence of any exposures of the 

 junction, it is impossible to say to what extent the amount of dip of 

 the two series differs. The complete absence of the Ordovician 

 formations from the district would prepare one to find a marked 

 difi'erence in this respect. The dip of the Grey Shales, however, in 

 the Bronsil district (where the sandstones are best exposed) varies 

 generally from 15° to 48^; that of the adjacent Llandovery Beds 

 ranges from about 17° to 60°. South of Bronsil the shales dip at 

 an angle of 40°, while the sandstone not far away dips at an angle 

 of 48°. These facts would seem to indicate that the dips in both 

 series are of the same order, and that, were actual junctions exposed, 

 the discordance between the two might not be perceptible in a 

 single section. Moreover, the behaviour of the line of junction as 

 it crosses the contour-lines (see map, PI. XIII) can hardly be 

 explained otherwise than by supposing that the plane of junction 

 of the sandstone with the shales dips everywhere into the escarp- 

 ment, at an angle approximately equal to that of the dip of the 

 May Hill Series ; or, in other words, that the Llandovery Beds 

 overlie the older series, with probably apparent conformity. 



In this connexion it must, however, be noted that, if (as is 

 practically certain) the main igneous belt in the Bronsil district 

 corresponds with the Coal Hill band of the districts on the south- 

 east, the beds of this horizon are appreciably nearer the 

 escarpment in the northern than in the southern part of the 

 ' Western Tract.' The line of igneous bosses in the Upper Grey 

 Shales (M 101, 101 «, & 102) approaches very near the escarpment 

 south of Martins, while on the north there seem to be no indi- 

 cations of its existence, unless M 247 denotes its reappearance 

 towards the east. This zone has probably passed underneath 

 the May Hill Beds north of Martins. Moreover, the area occupied 

 by the Upper Grey Shales broadens out towards the south, as seen 

 south of Coal Hill. These facts probably indicate that, as the 

 unconformable junction is followed from north to south, newer beds 

 belonging to the Grey Shales gradually make their appearance, 

 the Llandovery Beds slowly overstepping the zones of the Grey 

 Shale when traced northward. 



On the other hand, there is no evidence of an overlap of the 



