12 PBOF. E. J. GARWOOD AXD MISS E. GOODYEAR |_Voi. lxxiv, 



which crop out in front of the Harp-Inn Quarry. Again, the 

 micaceous greywacke which appears near Dolyhir Station may be 

 matched by the rocks of Sharpstone Quarry, east of Bayston, with 

 their included pellets of purple mudstone. Lastly, the matrix 

 filling the cracks and joints of the middle portion of the Bayston 

 Group on Lyth Hill is characterized by. the presence of black 

 ferruginous and bituminous material, and the same phenomenon 

 is conspicuous in the grits at Harp- Inn and Gore Quarries. 



In summing up the results of the comparative study of the 

 rocks in thin sections in the two areas, Dr. Thomas remarks : — 



A microscopical study of the rocks of the two regions reveals the fact that 

 the respective rock-types are comparable even in their minutest detail, and 

 their similarity may be reasonably accepted as an indication of practically 

 identical origin, mode of deposition, and geological age. 



The greywackes and grits north of Dolyhir Station and in Gore Quarry 

 not only have their green and red tints and general texture repeated in the 

 rocks of the Longmyndian of Lyth Hill and Bayston : but the deposits 

 correspond in their mineral composition, and in the character of the rock-types 

 represented by the larger included fragments. The highly-micaceous green 

 and red grits with their curiously-flattened mud-pellets find an exact parallel 

 in the Bayston Series of Sharpstone Hill. In these rocks the mica is of the 

 same general type throughout, being detrital in character, and consisting of 

 a minute intergrowth of chlorite, after biotite, with muscovite. 



The ordinary speckled grits and greywackes, with their characteristic 

 angular grains, abundant albitic and perthitic fragments, and plentiful detrital 

 garnets, may be matched in the same two areas ; thej also present a close 

 similarity to the speckled grits of the Broken Stones of the Horderlej^ 

 district. 



They have undergone the same type of alteration : namely, veining with 

 epidote and chlorite ; while a general epidotic character is a common feature 

 of the more compact varieties in both areas. Further, the occurrence of 

 hituminous epidotic veins that mark incipient brecciation in some of these 

 rocks, as at Lyth Hill and Old Radnor, again emphasizes the likeness that 

 •exists between the rocks of the two regions. 



In the case of the coarser grits, in the composition of which rock-fragments 

 play an important part, the analogy becomes still more striking : for now 

 soda-rhyolites with good fluxion- and perlitic structures, microlithic kerato- 

 phyres, fine-grained quartzites. and albitized basalts may be recognized. 

 Many of these rock-fragments from the grits of Old Radnor have such 

 definite characters that it would be easy to recognize them should they occur 

 in rocks of any other district ; it is thus interesting to find an exactly similar 

 assemblage, with the characteristic types well represented, in the grits of the 

 Bayston Series of the Longmynd and Lyth Hill. From Prof. Cox's descrip- 

 tion of the Brampton-Bryan deposits it would appear that those rocks have 

 been derived from sources similar to (or identical with) those that furnished 

 the material to the other areas. 



As has already been stated, the coarse grits of the district under description 

 are practically identical in composition with the matrix of the conglomerates. 

 It will follow, therefore, that if the grits are identical with those of the 

 Longmynd and of other adjacent areas of Longmyndian recks, we shall find 

 the same close (or an even closer) similarity in the pebbles forming the 

 associated conglomerates in the respective districts. This has proved to be 

 the case. The pink conglomerate that crops out south of Castle Nimble, 

 with its characteristic pink quartzite, soda-granites, soda-aplitcs. red-banded 

 rlryolites, and keratophyric r-oeks, may be matched with the middle (Durnford) 

 conglomerate of Lyth Hill, which contains practically the same assemblage of 

 rock-types. Basaltic rocks of like texture and similarly albitized are met 



