Vol. 56.] INLIER AT OLD EADNOR. 517 



aggregation of very minute tubes of equal size, which are apparently, but not 

 very clearly, polygonal. One of these fossils seems almost complete, the margin 

 being nearly entire. The remainder of the margin, as well as a great part of 

 the margin of another specimen, is irregularly serrated, as if corroded. A 

 third specimen in the slide is a fragment. The space between the fossils is 

 occupied by clear calcite : some of this is finely granular ; some is in fairly 

 large crystals ; and some of it displays a compound polygonal structure, suggest- 

 ing a Favosites. I think, however, that this is only mimicry, and that it is 

 really concretionary, consisting of aggregations of tubular bodies. That it is 

 not organic appears from its relation to the fossils. It is moulded to their 

 corroded edges, and has therefore been formed later. 



[560] Same locality. 



This specimen exhibits the same general characters, but fragments of unaltered 

 limestone take the place of the fossils. The fragments consist of a somewhat 

 dingy-looking groundmass of very minute particles of calcite. Scattered through 

 this groundmass are small bits of shells and crinoids. The pygidium of a 

 minute trilobite can also be detected. The space between the limestone- 

 fragments is filled with clear calcite, some of it showing the tubular structure. 



[561] Quarry on Yat Hill. 



The slide is selected as showing a junction between one of the pebbles of 

 grit and the limestone-matrix. Some of the limestone in contact with the grit 

 is unaltered, and is in places stained with brown matter which has found its 

 way along the plane of junction. Some of the matrix is changed to clear 

 calcite, and the tubular structure is also present. The quartz-grains of the 

 grit are very much broken, and the cracks are often filled with calcite, doubt- 

 less derived from the matrix. 



It would appear from the evidence of these slides that the altered 

 appearance of the rock is due to crushing, followed by the infiltra- 

 tion of carbonated water, which partly dissolved the limestone, 

 and redeposited it as clear calcite, either in well-formed crystals of 

 various sizes, or in aggregations of tubular concretions. 



The alterations in both grit and limestone are thus seen to be 

 due to the same causes — crushing and infiltration. Whether the 

 earth-movements producing the crushing are connected with the 

 Church-Stretton system of faults, I am not prepared to say. The 

 southerly dip in some of the micaceous laminae on Old Radnor Hill 

 would seem to point to a force acting from the south, but it is 

 possible that the crushing-forces have operated in different direc- 

 tions at successive epochs. 



It is perhaps hardly necessary to point out that there is no 

 evidence of the intrusion of igneous masses which could have 

 affected the rocks in question. The gabbro, dolerite, felsite, and 

 granitoid rocks of the Hanter and Stanner hills, which are only 

 -J mile to the east, lie on the south-westerly prolongation of the 

 axis of the Wrekin and Caer Caradoc ranges. Therefore they may 

 be presumably regarded as associated with pre-Cambrian masses 

 hidden by a superficial covering of Silurian sediments, even if they 

 are not all of pre-Cambrian age. They are quite Unlike the known 

 post-Silurian eruptive rocks of the region. The dolerite is similar 

 to that intruded in the Uriconian near Church Stretton ; the felsite 

 suggests the Uriconian itself ; and the granitoid rock is almost 

 certainly of still greater antiquity. 



