10 PROF. E. J. GARWOOD AND MISS £. GOODYEAR [vol. Ixxiv,. 



No conglomerates have been met with in the micaceous grits, 

 which crop out at the southern end of Yat Wood on the north 

 side of the railway ; but south of the line a grey quartz-conglomerate 

 occurs beneath the Woolhope Limestone on the east side of 

 Dolyhir Quarry (see inset-map, PL VII), while a similar rock, 

 probably a portion of the same bed, crops out round the northern 

 margin of Strinds Quarry, and is well exposed beside the footpath 

 leading from the quarry to Strinds Cottage. Fragments of this 

 conglomerate are also included in the thrust masses of limestone 

 and Pre- Cambrian rocks which are exposed along the north-eastern 

 face of the quarry (D). A further fragment is exposed in the old 

 quarry, below the bend in the road north-east of Strinds Farm, 

 where it has been brought in by the north-and-south fault which 

 brings up the Pre- Cambrian rocks on the east. Pebbles of the grey 

 quartz have here been torn from the conglomerate, and plastered 

 along the face of the fault-plane to form a derived thrust-con- 

 glomerate (PI. III). 



The materials of which these Pre- Cambrian sediments are com- 

 posed appear to have originated from several sources, including 

 as they do various types of sedimentary, igneous, and metamorphic 

 rocks. In their general characters these Pre- Cambrian deposits 

 differ from the typical marine sediments of later formations, and 

 appear to resemble more nearly certain lenticular detrital deposits, 

 such as the JS T agelnuh of the Alps, to which a fluvio-lacustrine 

 origin has usually been assigned. 



In concluding this description of the Old Radnor Pre-Cambrian 

 rocks, we may add that no traces of organisms have been met with 

 in any of the rocks of the series. 



(b) The Position of the Old Radnor Rocks in the 

 Longmyndian Series. 



From the above description of the grits and conglomerates of 

 Old Radnor, it is obvious that Murchisons view, adopted also in 

 the Geological Survey map, that this series represents the May-Hill 

 Sandstone or JPentamerus Grit of the Presteign district, metamor- 

 phosed by subterranean intrusions of igneous rocks, cannot be 

 sustained, and that Callaway's suggestion l that the series re- 

 presents a mass of Longmyndian rock jutting up amid Silurian 

 strata, is correct. The question still remains Avhether this Old 

 Radnor series can be correlated definitely with any portion of the 

 Longmyndian of the Bay r ston area. The presence of, at least, two 

 different types of conglomerate intercalated in the red and green 

 grits, taken together with the occurrence of micaceous greywackes 

 and* bands of line crimson mudstone, gives a definite character 

 to the Old Radnor series, which recalls very clearly certain portions 

 of the normal Longmyndian succession. Prof. Charles Lap worth, 

 as the result of his work in mapping the Longmyndian rocks of' 



1 Q. J. G. S. vol. lvi (1900) p. 514. 



