ON TIIK AnClI.EAN HOCKS OK GUEAT BUITAIK. 



533 



taininp: 

 •drated 

 itiracter 



3 (or an 

 c, with 

 overack 



kt-s and 



altered ; 



tliey are 

 B jrabbro, 

 mbers of 

 and the 

 abase -is 

 c already 

 , \vc may 

 cks which 



,bo Tjizavd 

 ■xposed ii> 

 i Porthalia 

 o-schist ir. 

 rd of fault 

 d one. At 

 are faaUed 

 have more 

 by parallel 

 ly %Yith tlie 

 are faulted 

 t a mile to 

 .ents of the 

 ,t unlike a 

 [period, and 



ba occiipit^^^^ 

 Iroin cast to 

 I are chiefly 

 Ixposcd two 

 kloritic rock 

 tock. in tlie 

 Icbist occur, 

 ions macro- 

 b pale olive- 

 la, probably 



UuMnctiimov- 

 \(,h(art.Joun, 



je\ d'cfll"'.!"'"' 

 nost v,ilu;i!'l' 



pai'agonite or margarodite — with specks of iron peroxide, and possibly a 

 little graphite, with a grannie or two of epidoto. In the bands associated 

 with the chloritie rock are a few gmins which may possibly be felspar, but 

 have rather more resemblance to kyanite. The chloritie rock has for its 

 most abundant mineral a chlorite, withepidote, quartz, and sometimes the 

 mineral just described (kyanite?), and with occasional calcite and iron 

 poi'oxido. As mentioned above, there are several minor varieties. I am 

 not aware th.at there are any igneous rocks intrusive in this series. 



Kcideno'n of Geologic Age. — The stratigraphy of this district is difficult. 

 The bods have been throv.-n into a series of repeated gigantic and almost 

 vertical folds, and there is very distinct evidence that this disturbance 

 has been subsequent to their metamorphism. It is thus extremely difficult 

 to say whether there is a thick bed of mica-schist both above and below 

 till) chloritie schist ; or whether the lowest rock seen is the interbanded 

 chloritie- and mica-schist, and the upper mica-schist is repeated by the 

 folding, I incline to the latter opinion. The metamorphic series is 

 hounded on the north by a fault, and succeeded by a slaty series, generally 

 of a dark colour, which from the fineness of its argillaceous materials and 

 tlic liyponictamorphic effect of the pressure to which it has been subjected, 

 often has a considerable macroscopic resemblance to the true mica-schist, 

 but can be I'oadily distinguished under the microscope and, after careful 

 examination, even in the field. This rock is considered to be of Devonian 

 ago.' The date of the great folding is no doubt post-Carboniferous aud 

 pre-Triassic. 



In addition to the above-mentioned rejrious. true srneiss of a marked 

 Archaean type has been described, by Mr. A. H. Hunt,- from the reefs 

 about the Eddystone Lighthouse, and specimens of coarse gneisses have been 

 dredged up from various parts of the Channel off the South Devon coast 

 Gneisses, of a type which occurs in the lower part of the Archocan series, 

 occur in the Channel Islands, and those of Guernsey have been described 

 by the Rev. E. Hill and myself.^ 



(3.) Malvern Ililb. — We are indebted to Mr. H. B. HoU"* for a care- 

 ful description of the petrology of this district, and some analyses of the 

 rocks were made by the Rev. J. H. Timins,* bnt at present no complete 

 st\uly of their microscopic structure has been published. The ridge of 

 Arcliiran rock runs nearly north and south, and is a little more than seven 

 miles in length. The greatest breadth from east to west is about half a 

 juilc, but it is commonly less. The strata strike roughly from NW. to 

 SE.. and are inclined at high angles, being often nearly vertical ; but it 

 is probable that those at the southern end are higher in the series than 

 tliiiso at the northern. Some isolated bo^.ses protrude through Silurian 

 rocks still further to the north, the last exposure at a distance which 

 makes the entire length of the area about sixteen miles. At the northern 

 end are granitoid gnei-sses, generally coarse, occasionally almost binary 

 compounds of quartz and reddish felspar, but more commonly containing 

 in addition dark green hornblende or blaokish mica, and ao passing into horn- 

 blendic or micaceous schists. In the southern part the gneisses become finer- 

 grained and more thinly bedded, the schists more frequent ; mica, perhaps, 

 being more common and conspicuous than in the north ; chlorite aud 



'^ I'or a detailed description of the district, soc my paper, Q J. G. S., vol. xl. p. !• 



" Sec papers in Tnnis. Jh-ronshirr Am>c. 1880-4. 



' Q. J. G. S., vol. xl. p. 404. * <J. J. G. S., vol. xxl. p 72, 



■' ','• J. G. S., vol. xxiii. p. H:,2. 



