Vol. 54.] OP BOTJLAT BAT (jERSEr). 107 



contrasted with a practical identity in change of curvature of each 

 crescent in correspondence with that of the edge of the specimen/ 

 seem significant as to their origin. Some other instances are not 

 less interesting. Occasionally one finds a nodule in which an 

 outermost laj^er is easily separable from the rest, peeling away in 

 flakes so as to leave a fresh and fairly smooth surface. Sometimes 

 this tendency is pronounced, as in the following : — 



Internally to the outer coat or layer (| inch thick) and 

 about g inch nearer the centre, the pyromeride being roughly 2^ 

 inches in diameter, a distinct line about y^ inch across, extending 

 at least halfway round the nodule, is clearly visible. Not only so, 

 but about '45 inch nearer the centre is another, not quite so regular 

 as the last, but still plainly to be seen. At one place immediately 

 on the outer side of the second crack, there is a concentric combined 

 with an approach to a radial structure, but the nodule does not 

 difi*er materially from those previously described. Microscopically 

 these cracks are not so conspicuous as might have been supposed, 

 for, instead of forming a continuous and evenly-bounded curve, the 

 appearance is only one of incipient rupture, apparently consisting of 

 a series of small sinuous cracks. Sometimes the formation of the 

 spherical surface has resulted in the separation of two otherwise 

 closely-united pyromerides, which lie to one another in the relation 

 of cup and ball, inequalities of the one being reproduced in the 

 other ; the ' ball ' in fact consists of two undiff'erentiated pyromerides, 

 an arrangement plainly shown also in the concave cup, which, 

 besides reflecting minor inequalities, consists in the same way 

 of two spherical surfaces. The above instances are from pyrome- 

 rides obtained from the cliff on the northern side of the jetty. A 

 similar structure from the Tete des Hougues deserves a few words. 



This, or as much of it as can be seen, consists of a large pyro- 

 meride imperfectly marked off from the surrounding rock. At 

 what would be the centre, if the whole were visible, is a mass 

 of quartz surrounded by reddish felstone, suggesting, more than 

 absolutely showing, a concentric structure. This is followed 

 by a large circular crack, nearly ^ inch across, which after 

 subtending an angle of 45°, suddenly changes its direction so as to 

 represent roughly the figure B. Externally to this again is appa- 

 rently the outer zone of the pyromeride, which in turn is surrounded 

 by the body of the rock. This structure, due no doubt to the 

 results of unequal cooling, is precisely the same as that described 

 by Prof. Bonney from North Wales.^ (See fig. 1, p. 108.) 



Before going further, it may be well to see whether any evidence 

 of a confirmatory character can be found. 



In the harbour itself, below the road leading to the jetty, there 

 are hard, greenish, greyish, and drab-coloured felstones, which in 



^ In this slide, in addition to the two crescents, there are at least twenty 

 breceiation-veins of different ages. Despite these manifold opportunities, 

 decomposition has failed to produce any effect ; but see G. A. J. Cole, Quart. 

 Journ. Geol. Soc. vol. xlii (1886) p. 183. 



^ Quart. Journ. Geol. Soc, vol. xxxviii (1882) p. -295. 



