ON THE ARCH.EAN ROCKS OF GREAT BRITAIN. 533 



paragonite or margarodite — with specks of iron peroxide, and possibly a 

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

 with the chloritic rock are a few grains which may possibly be felspar, bnt 

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

 most abundant mineral a chlorite, with epidote, quartz, and sometimes the 

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

 peroxide. As mentioned above, there are several minor varieties. I am 

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



Evidences of Geologic Age. — The stratigraphy of this district is difficult. 

 The beds have been thrown 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 

 the chloritic schist ; or whether the lowest rock seen is the interbanded 

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

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

 bounded 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 

 the hypometamorphic effect of the pressure to which it has been subjected, 

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

 but can be readily distinguished under the microscope and, after careful 

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

 age. 1 The date of the great folding is no doubt post- Carboniferous and 

 pre-Triassic. 



In addition to the above-mentioned regions, true gneiss of a marked 

 Archaean type has been described, by Mr. A. R. Hunt, 2 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 Archaean series, 

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

 by the Rev. B. Hill and myself. 3 



(3.) Malvern Hills. — We are indebted to Mr. H. B. Holl 4 for a care- 

 ful description of the petrology of this disti-ict, and some analyses of the 

 rocks were made by the Rev. J. H. Timins, 5 but at present no complete 

 study of their microscopic structure has been published. The ridge of 

 Archaean 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 

 mile, 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 

 those at the northern. Some isolated bosses 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 gneisses, generally coarse, occasionally almost binary 

 compounds of quartz and reddish felspar, bnt more commonly containing 

 in addition dark green hornblende or blackish mica, and so passing intohorn- 

 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 and 



1 For a detailed description of the district, see my paper, Q. J. G. S., vol. xl. p. 1- 



2 See papers in Trans. Devonshire Assoc. 1880-4. 



3 Q. J. G. S., vol. xl. p. 404. * Q. J. G. &, vol. xxi. p. 72. 

 5 £. J. G. S., vol. xxiii. p. 352. 



