Vol. 56.] BUNTER PEBBLE-BEDS OP THE MIDLANDS. 291 



number about thirty. I have had a few more sliced, and written 

 a description of all ; but, as many are of a commonplace character, I 

 think that it will suffice to give a brief general summary, with a 

 more detailed account of a few characterized by features of special 

 interest. 



These pebbles vary from subrotund to very well rounded ; com- 

 monly they do not exceed about a couple of inches in diameter, 

 though occasionally they may attain 3 or 4 inches. In texture 

 they vary from perfectly compact to very minutely granular, 

 one or two being almost microgranites, exhibiting in fact all the 

 forms covered by the field-term f elstone. The majority, especially 

 of the more compact, contain grains of quartz, rather sparsely 

 distributed, and about as big as the head of an ordinary pin, which 

 is often found to be corroded by the groundmass. Eelspar also is 

 present, commonly in crystals measuring about y 1 ^ inch across, 

 but in one or two specimens it is more than | inch. It is generally 

 too much decomposed to allow of the species being determined 

 on microscopic examination. A few specimens contain a dark 

 mineral — either hornblende or tourmaline ; in one or two biotite is 

 present. The matrix in the majority is red, generally pale rather 

 than dark, and some of the latter tint evidently are more basic 

 than the ordinary kinds. In others it is' grey or greenish-grey. 1 

 In fact, the collection includes devitrifled rhyolites, dacites, felsites, 

 and porphyrites ; none of them, I think, being basic enough to be 

 called basalts, and the majority distinctly acid. 



A few specimens deserve a little fuller notice. One, a pebble from 

 Style Cop nearly 3 inches in diameter, is a compact cherty-looking 

 rock, traversed by thin quartz-veins. With ordinary light under the 

 microscope it resembles a glass in which slightly greyer streaks 

 are indicative of a fluxional structure. With crossed nicols the 

 rock proves to be microcrystalline, as if it were entirely composed 

 of chalcedonic quartz, the largest grains not exceeding *004 inch in 

 diameter. Scattered in this as a matrix are a few three or four 

 times that size, which in outline resemble felspar, though they are 

 now composed of microcrystalline quartz. I observe a certaiu 

 resemblance to specimens from Treffgarn and lloche Castle (Pem- 

 brokeshire) which are now admitted to be acid volcanic rocks, 

 subsequently affected by siliceous springs. 



Another specimen (from Baland's Pool Pit) is unique. The matrix 

 is very dark and compact, like a devitrifled glass ; this is irregu- 

 larly crowded with reddish spherulites, often nearly -2 inch in 

 diameter. These, on microscopic examination, appear of a brownish 

 colour, opacite being deposited between the radii. They are often 

 composite, sometimes broken, being either actual fragments or re- 

 cemented. A few crystals of felspar are present, mostly orthoclase, 

 in one instance showing a granular structure, with some grains of 

 quartz, more or less angular ; these, in one or two cases, are pierced 



1 One with a compact grey matrix, in which are small grains of quartz and a 

 small whitish felspar, is numerically commoner than the red kinds. 



