part I] ON THE GEOLOGY OF THE OLD RADXOK DISTRICT. 5 



(a) The Pre-Cambrian (Longmyndian) Rocks. 



These rocks occupy the greater portion of the northern half of 

 the inlier. They form the whole of Old Radnor Hill (PI. II) 

 with the exception of the north-western, southern, and south- 

 eastern margins, where narrow strips of limestone have been let 

 in by faults. They also occupy the district north and west of 

 St. Stephen's Church, and extend southwards as far as the fault 

 which runs immediately north of Vat Farm. South of this 

 fault the outcrop continues with an average width of about 

 200 yards in a south-westerly direction, through the eastern portion 

 of Yat Wood, to the railway, where a further exposure of Pre- 

 Cambrian rocks emerges from under the limestone north and 

 west of the station. The beds reappear on the south side of 

 the line, and occupy the lower slopes of the rising ground which 

 forms the elevations known as Dolvhir and Strinds, whence they 

 can he followed round alone the eastern side of Dolvhir Quarry. 

 Several small pitches are also met with on the north side of 

 Strinds Quarry, where they have been thrust up into the limestone, 

 and a similar thrust-block has recently been exposed by quarrying 

 operations in the north-western corner of Yat- Hill Quarry, north 

 of the railway. The rocks consist of pink and green sjreywackes 

 and grits, together with occasional bands of coarse conglomerate, 

 the series being essentially a sedimentary one throughout. The 

 apparent strike of these Pre-Cambrian rocks is roughly parallel to 

 the longer axis of the inlier, that is, north-north-eastwards, with 

 a high but variable dip to the we«t and west-north-west — that is to 

 say. the grain of the country runs in this direction. If, however, 

 an attempt is made to ma}) the different rock-types, it is not found 

 possible to follow any individual band continuously for more than a 

 short distance, and this is usually true of the conglomerates as well 

 as of the finer-grained deposits. The group, as a whole, really 

 represents a crush-breccia on a large scale, although some of the 

 fragments are of considerable size. The conglomerate-bands, as 

 might have been expected, have yielded less readily to pressure 

 than the finer sediments, and also offer greater resistance to 

 weathering: they can. therefore, be more readily traced than the 

 finer sediments. These conglomerates, however, include layers of 

 finer material, and this fact enables the dip and strike of the 

 individual outcrops to be ascertained with a fair degree of certainty. 

 In this connexion it is noteworthy that, with one exception 

 -(namely, the faulted patch immediately north of Stone's Farm). 

 all the conglomerate outcrops strike in a general northerly direc- 

 tion. This dominant direction of the grain of the country is 

 obviously the result of the last important set of movements that 

 have taken place in the district, though the rocks had evidently 

 undergone considerable crushing at a much earlier period. 



It is impossible, therefore, to draw up a table of the beds, or to 

 be certain of the true order of succession in any portion of the 

 district. The dip, when it can be ascertained, appears to be 



