36 



ON THE POEPHi'RITIC ROCKS OF THE ISLA^'D OF JEESET. 



to be considered as synchronous with the purple conglomerates of 

 the Cotentin — that is, with the ver}- base of the Silurian formations. 

 On this view I could easily see that the ])orphyritic series of Jersej' 

 might represent something equivalent to the oldest felsites of Xorth 

 Wales. But having never visited the ground, and being desirous 

 of correcting my error b}' actual inspection of the rocks in situ, 

 I paid a visit to Jersey last summer. 



At the first glance I could perceive that the porphyritic series, 

 instead of being discordant with the schists, is intimately connected 

 with that formation and partakes of its general strike and dip. At 

 the base of the eruptive mass, tuffs and breccias prevail, which 

 under the microscope prove to be mainl}- tuffs of porphyrites. Such 

 are the rocks at Havre-Giffard, the so-called metamorphic schists, 

 with large crystals of felspar, at the Imperial Hotel, and also the 

 rocks which are worked at Stephen's Mill for road-material. Then 

 comes, at Anne Port, a blood-coloured porphyritic mass, which 

 looks quite like a red quartziferous felsite, but which, microscopic- 

 ally examined, proves to be a porphyrite with a large admixture of 

 iron-bearing quartz, becoming in some places a true red jasper. 

 This mass underlies the reddish felstones, with well-marked 

 columnar structure, of La Crete and Archirondel, while the 

 pyromerides of Boulay Bay form the top of the series, being, at the 

 Tete des Hougnes (as clearly stated by the Be v. C. oS^oury, in his 

 ' Geologic de Jersey '), immediately succeeded by the first purple- 

 coloured layer of the Bezel conglomerate. 



I do not intend to enter here into a more detailed study, which I 

 am preparing for the Geological Society of France. But I thought 

 it my duty to do justice to the geologists who had long ago 

 recognized the true character of those " old rhyolites," which, from 

 mistaken theoretical views, I had been led to regard as Permian 

 eruptive rocks, although, in fact, when carefully examined, they 

 exhibit very little in common with the true Permian porphyries of 

 France or of Saxony. 



Discussion. 



Mr. E. Hill considered the Author's former opinion was the 

 natural consequence of Ansted's views. Messrs. Davies and Bigot's 

 work had entirely overthrown these. He agreed with the Author as 

 to the relation between the argillites and the porphyritic rocks, 

 and awaited with interest the further information promised. 



