HARDWICKE'S SCIENCE-GOSSIP. 



243 



shooting, and noticed two Davus and a few Aglaia, 

 but much worn and in the tatters of their former 

 gaiety. Since then I have shot nearly every day over 

 a wide range of moor and mountain, but have come 

 across few moths and no other butterflies of conse- 

 quence. 



One proof of the effect of the very heavy rainfall 

 in the Highlands was afforded in the case of Vanessa 

 tirtioE. Early in June there were thousands of the 

 larva of that butterfly on the nettles, but before they 

 were full grown, they were swept from their feeding- 

 places and drowned by hundreds, and now there are 

 very few perfect insects either on the wing or hiber- 

 nating. 



I am glad to see, from several very interesting 

 articles which have recently appeared in Science- 

 Gossip, that the lowland collectors have had better 

 weather and sport than we have had up here. 



Edwin Lester Arnold. 



Bahiyle, Blairgowrie, N. B. 



A VISIT TO A WELSH STONE-QUARRY. 

 By E. Halse, A.R.S.M. 



THE quarry about to be described is only a few 

 hundred yards from the small village of 

 Pontrhydfendigaid (" Bridge of the Blessed Ford"), 

 situated midway between Lampeter and Aberystwith. 

 The face of the quarry shows a series of beds of clay- 

 slate, of Lower Silurian age, striking at a low angle 

 to the N.N.W., and dipping away from us to the 

 W.S.W. Organic remains are by no means common in 

 this quarry, or in the surrounding formation ; indeed, 

 the ordinary observer would soon come to the con- 

 clusion that it was entirely destitute of them ; but the 

 geologist, after careful search, would doubtless succeed 

 in finding one or two specimens of graptolites, and 

 other apparently insignificant fossils. Without look- 

 ing for any ' medals ' and ' footprints ' of former 

 epochs, let us examine the quarry as it has been 

 opened out, collect as many data as we can, and 

 endeavour to form therefrom rational conclusions with 

 regard to its history, and the history of the surround- 

 ing strata. 



By means of a clinometer we see that the beds dip, 

 on an average, at an angle of 39°. The beds are of 

 variable thickness, 12, 8, and even as little as ig 

 inches. Layers of quartz are seen between some of 

 the beds, and we note that little veins of the same 

 mineral run through the beds, generally parallel to 

 the larger layers of quartz between the beds, and 

 therefore parallel to the planes of the beds of clay- 

 slate themselves. But this parallelism is not invariable; 

 some veins are seen to run cross-wise, meeting the 

 more parallel ones at an acute angle (fig. 139). These 

 veins are also of inconstant thickness, one we measure 

 is Ig inches thick, widening to the N.N.W. to as 

 much as 2\ inches ; others measure I inch, ifj inches. 



3, ^> 53 inch, down to mere lines or threads. On 

 examining a large vein or layer of quartz, we find it 

 to be more or less crystalline in appearance, and in 

 parts very tender, rotten, and of almost a cellular 

 structure, and discoloured with black earthy matter. 

 As an indistinct line is seen to run roughly down the 

 centre, and the vein breaks easily into two portions 

 along the central line, it is evidently composed of two 

 layers. Here and there little cavities or " vughs" are 

 conspicuous, lined with rather large crystals of quartz. 

 But there is another mineral in these veins — iron- 

 pyrites — visible to us as clusters of little crystals, and 

 occasionally as rather large isolated ones. In places 

 we observe that there is an accumulation of iron- 

 pyrites, whilst in other parts of the vein there is little 

 or none of that constituent. The iron-pyrites in the 

 rotten portions of the veins is discoloured, and is, in 

 fact, in a more or less oxidised or decomposed con- 

 dition. The smaller veins, and parts of the larger 

 ones, are composed of milk-white quartz, with here 

 and there very bright and metallic crystals of iron- 

 pyrites. Nothing has affected these smaller veins, 

 and, on close examination, they appear to consist of 

 two or even more layers of quartz, similar to the 

 larger ones. If we examine the crystals of iron-pyrites 

 with a lens we shall find them to be in the form of a 

 cube, more or less developed. In most cases little 

 shoulders, as it were, of the cube peep out, and a 

 series of deeply indented lines or striations are seen 

 running parallel with the edges, and twin crystals are 

 not uncommon. The striae on two adjacent faces are 

 at right angles to each other (fig. 140). Now it 

 appears that when iron-pyrites is crystallising out, it 

 has a tendency to form, besides the cube or primary, 

 and many other forms, the form known to mineralo- 

 gists as the pentagonal dodecahedron (fig. 141). The 

 result is, as it were, an oscillation between the two 

 forms, consequently these striae are produced ; but 

 the general form taken is that of the cube, as the 

 tendency to form a cube in this instance, was much 

 greater than that to form a pentagonal dodecahedron. 



In fig. 142 we have an interesting case of one 

 little vein connecting two larger ones. 



We cannot fail to notice that the beds break up 

 along planes practically at right angles to those of 

 bedding ; the quarryman is thus enabled to take 

 away the stones in large blocks. These planes per- 

 pendicular to the bedding are the joints, 



A careful examination will soon reveal to us another 

 series of lines (fig. 143 jt), dipping towards us to the 

 N.E., and making variable angles with the beds of 

 clay-slate. Here the angle is 50°, there 48", and in 

 one place as high as 75°. We notice, however, that 

 these lines are constant with regard to each other — 

 they are parallel — and, if they deviate at all from this 

 the deviation is only local, and apparently due to local 

 causes. These lines are very indistinct in the dry 

 rock, but they are easily perceptible where the rock 

 is wet. If we test a portion of the rock with a 



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