"Vol. 54.] THE PYKOMERIDES OP BOULAT BAY (jERSET). lOi 



7. On the PrROMEEiDEs of Botjlay Bay (Jersey). By JoHif 

 Parkinson, Esq., F.G.S. (Read December 15th, 1897.) 



[Plate VII.] 



Contents. p^^^^ 



I. Introduction lUl 



II. Grenerai Characteristics ot the Rock 101 



III. Comparison with other Districts 110 



IV. Pyromerides with relatively large Quartz-enclosures 116 



I. Introduction. 



The acid lavas forming the more easterly part of the northern coast 

 of Jersey have been the subject of investigation by many geologists. 

 M. de Lapparent, in a note on the eruptive rocks of the Isle of 

 Jersey ^ published in 1884, summarized these accounts, and his 

 paper was extensively quoted by M. Noury in his ' G^eologie 

 de Jersey,' published a few years later, the quotations including 

 those paragraphs which relate to the work of previous authors. 

 The earliest is that of Macculloch, in 1817, in which a hornstone- 

 porphyry is noticed from this neighbourhood. A geological map of 

 the island was published by A. Transon ^ in 1851, in which the 

 northern half of Boulay Bay is represented as being occupied by 

 porphyries, the southern by grit, while the line of demarcation 

 between the latter rock and the more easterly conglomerate is 

 correctly indicated. In 1879 the ' spherular character ' of the 

 rhyolites of Boulay Bay was briefly noticed by Mr. Thomas Davies, 

 principally from specimens supplied bo him by l)r. Dunlop, of Jersey.^ 

 M. JSToury, in his work, supplements his quotations from M. de 

 Lapparent with additional observations of his own on the charac- 

 teristics and origin of the structures exhibited by the rhyolite, at 

 the same time giving a map wherein the principal locality at which 

 pyromerides occur is indicated. Since the publication of Noury's 

 book, a few notes on Jersey have been intercalated in some general 

 observations * on the Channel Islands by M. A. Bigot; and the Eev. 

 Edwin Hill has also referred to both the rhyolites and neighbouring 

 conglomerates in his account of the geoJogy of Alderney.^ 



II. General Characteristics of the Eock. 



Almost in the centre of the Bay, at the crags marked as L'Islet, 

 occurs a darkly-weathering red felstone, typical of much in the 

 vicinity. Elow-structure is conspicuous, the surfaces being in 

 general straight, though occasionally wavy, and in a few places 

 showing complicated flow-contortions on a small scale. Just below 

 high-water mark, the fine flow gives place to a coarser banded 

 structure. 



1 BuU. Soc. geol. France, ser. 3, vol. xii (1884) p. 284. 



2 Annales des Mines, ser. 4, vol. xx (1851) p. 501. 



3 Min. Mag. vol. iii (1879) p. 118. 



* Bull. Soe. geol. France, ser. 3, vol. xvi (1888) p. 412. 

 5 Quart. Jouru. Geol. Soc. vol. xlv (1889) p. 380. 



