Vol. 54.] OP BOFLIT BIT (jERSEY). 103 



examinatioa of fche rest of the slide brings out, however, the fact that 

 it is truly igneous. The red fragments differ principally in a ferri- 

 ferous staining. 



The pyromerides which form the subject of the following notes, 

 and are so characteristic of the Boulay Bay rock, occur in two 

 principal positions ; the first, and certainly the best for general 

 purposes of study, is that indicated in JSToury's map on the northern 

 side of the jetty and a few hundred yards from it. Here in places 

 the cliffs are practically made up of pyromerides, clustered thickly 

 together, and producing the same remarkable effect as in North 

 Wales and elsewhere, owing to the fact that they resist weathering 

 agencies better than the rest of the rock. 



The second locality is just above high-water mark at the Tefce des 

 Hougues farther east, and almost at the point where the rhyolit3 

 is overlain by the conglomerate which forms the north-eastern 

 corner of the island. 



It may be well, before considering the pyromerides themselves 

 more closely, to notice the relation that they bear to the rock in 

 which they lie and to each other. A series of specimens from the cliff- 

 top on the northern side of the jetty, where the pyromerides are 

 most abundant, seems to show this best, though it is b}^ no means 

 intended to suggest that the stages represented indicate more than 

 one of the methods by which these nodules have be9n produced. 



The rock, which shows traces of flow-structure often markedly, 

 is traversed in places by bands having a different appearance from 

 that of the rock immediately surrounding them. These bands are 

 obviously due to a difference in the nature of the material, as in the 

 common case of a banded lava. 



A. piece of one of these, about 1| inch in breadth, was detached 

 from the softer greenish-grey rock which surrounded it. As this 

 was taken from a flat surface, one surface of the band was of course 

 also flat ; but the other and buried side was roughly cylindrical, 

 so that a transverse section would give an approximately semicircular 

 outline. Examining the flat surface more closely, it is seen that its 

 edges are not quite straight lines, but become slightly indented in 

 places, thus forming a series of flat arcs. There are developed also 

 small knobs or lumps, which give a mammillated appearance to the 

 cylindrical surface. 



In a thin section, the structure of this flow-band is identical with 

 that of the pyromerides to be described later. In transmitted light 

 it is rather structureless, of a light brown colour, with innumerable 

 black microliths^ having no relation to the faint radial growth 

 which is just visible, although they have a decided parallel tendency 

 among themselves. Between the two nicols, the section resolves 

 itself into a mosaic of separately polarizing, but extremely irregular 

 areas, the size of which varies considerably in different parts of the 

 slide. The radial structure is, so far as can be seen, normal to the 



1 See Quart. Journ. aeol. Soc. vol. xlv (1889) p, 258. 



