Vol. 51.] THE COUNTKT ABOUND FISHGUARD. 185 



basalt-glasses, variolites, and marginal modifications of diabase 

 described by Cole and Gregory, 1 Judd, 2 Groom, 3 and otbers ; and we 

 shall see immediately bow closely linked they are with certain others 

 which bear a strong resemblance to the variolitic rocks of the Lleyn 

 peninsula in Forth "Wales described by Miss Raisin. 



The second variety of this group of rocks, while possessing the 

 general appearance and constituents of the tachylytic variety, is as 

 a rule destitute of the groups of parallel augite-crystallites. But 

 no hard-and-fast line can be drawn between the two varieties, as 

 many intermediate forms occur. The characteristic feature, however, 

 of this second variety is the tendency of the felspathic fibres and 

 crystallites to group themselves into spherulitic aggregates (PI. VI. 

 tig. 2). These aggregates appear as semi-opaque greyish spots of 

 small size, under the microscope, and are roughly spherical in shape. 

 They consist of minute radiating felspathic fibres, with a ring of 

 granules and. dusty material round the whole spherule. Most of them 

 have indefinite boundaries ; some are axiolitic and have formed around 

 felspar-crystals. With crossed niools an indistinct black cross is 

 visible in some of the spherulitic growths. Various stages in the 

 development of these radial groups are to be found in a series of 

 slides which I have had prepared. The most perfect examples are 

 from Garn Pechan, adjoining Garn Pawr, where the tachylytic 

 variety just described is found. The radial groups are best shown 

 in [257], [226],, [283], where most of the spots have definite bound- 

 aries of augite-granules and dusty material. In other slides — [263], 

 [227], [303] — the spots are more irregular and less clearly marked 

 out, while the felspar-crystals in the rock are fringed with divergent 

 felspathic fibres. 



Through the kindness of Miss Catherine Raisin I have been able 

 to examine her slides of variolitic rocks from the Lleyn ; and I 

 readily identified the radial structures in my Pembrokeshire rocks 

 with the ' incipient varioles ' mentioned by her. The structures 

 are undoubtedly identical, and the spheroidal diabase of Porth-din- 

 Lleyn, in which these incipient varioles are well shown, has features 

 exactly similar to those in the spheroidal diabase [283] of Porth 

 Lleuog, Strumble Head. The Porth-din-Lleyn rock has been 

 described by Miss Raisin, 4 and I have had the privilege of seeing 

 the actual slides and of thus comparing the structures side by side. 

 Hence we may chronicle the discovery of another British locality 

 for variolitic rocks in addition to those already known in Anglesey, 

 Co. Wicklow, Co. Down, the Lleyn peninsula, and Carrock Pell. 

 However, the variolitic structures seem to be merely incipient and 

 rudimentary in all the Strumble Head examples, and they are 

 rarely visible macroscopically. The varioles, also, in the latter 

 rocks have not been found as pea-like bodies on weathered surfaces, 

 as is the case in the Lleyn examples ; and ferruginous varioles of 



1 Quart. Journ. Geol. Soc. vol. xlvi. (1890) p. 295. 2 Md. vol. xxxix. (1883) p. 444. 

 3 Ibid. vol. xlv. (1889) p. 298. 4 Ibid. vol. xlix. (1893) p. 155. 



