512 DR. C. CALLAWAY ON - THE LONGMYNDIAN [Aug. I9OO,- 



1. Unconformity between the Woolhope Limestone 

 and the Old Radnor Series. 



On the north-eastern side of Yat Hill, an elevation coalescing 

 with Old Radnor Hill on the south-west, within 90 yards 

 of a slaty outcrop of the Old Radnor Series, the Woolhope Lime- 

 stone appears at the surface. One bed of it seems to dip in a 

 westerly direction, and as no limestone is seen to the east of it, this 

 is probably the base of the Woolhope Series. It is crowded with 

 rounded and angular fragments of a grit which bears a marked re- 

 semblance to the arenaceous part of the Old Radnor Group. The 

 matrix of the fragments is pure limestone, containing abundant 

 specimens oiFavosites of the gothlandica-tyjye. Near at hand on the 

 south is a large quarry, on the southern side of which a similar con- 

 glomerate occurs in wall-like masses 6 to 9 feet high, but no clear 

 dip could be determined in it, nor in any part of the limestone of the 

 quarry. The conglomerate is of a most pronounced type, the clear 

 limestone-matrix being packed with fragments of the grit, most of 

 them well-rounded. Favosites also occurs in the limestone of the 

 quarry. These facts would seem to suggest a shore, margined by a 

 pebble-beach, forming a foundation for a fringing-reef. 



2. Lithological Characters of the Old Radnor Series. 



Grit is the prevailing rock, but in a quarry near the church there 

 are some associated slaty bands. They are approximately vertical, 

 with a north-and-south strike, and are somewhat contorted. Fine- 

 grained grit and indurated flinty mudstone occur near the western 

 margin of the Old Eadnor mass, 90 yards east of the Yat Hill 

 limestone. The beds dip westward at a moderate angle. These 

 are the only exposures of the Old Radnor Series in which bedding 

 could be detected. I searched Old Radnor Hill from end to end, and 

 could find nothing but grit, without clear stratification. Towards 

 the southern end of the ridge there is a fair proportion of mica, 

 much of which lies in planes dipping at a low angle to the south. 

 Under the microscope, a great part of this mica is seen to be of 

 secondary origin, being in unworn and unbroken crystals, which 

 are moulded to the angles of the other minerals of the grit. This 

 apparent lamination would seem, therefore, to have no connexion 

 with the original sedimentation of the rock. 



The obliteration of bedding in the Old Radnor Series is due to 

 crushing, of which very clear proof can be seen in many places. One 

 of the best sections for studying the crush-phenomena is in a large 

 quarry at the north-eastern end of the ridge. The grit is traversed 

 by joints striking in all directions. The joint-surfaces are stained 

 with a black substance, and are often slickensided. The motions 

 which produced the slickensides have not always acted towards the 

 same point of the compass. In some places the rock is crushed 

 into a breccia, with fragments of various sizes, some of them almost 

 microscopic. The rock is brecciated also on the northern slope of 

 the hill, and at many points along the summit- ridge. Sometimes 



