1 72 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 20, 



metamorpliosed during the Lower Silurian period. The foliation 

 of the Anglesea rocks is probably a result of this metamorphism, and 

 this may account for the fact- that this foliation lies not altogether, 

 but exceedingly frequently, in or approximately in the direction of the 

 lines of bedding ; for it must be recollected that the principal cleavage 

 of the Silurian and Cambrian strata of Wales took place at a period 

 long subsequent to the date of the volcanic and supposed meta- 

 morphic phsenomena. The whole of the strata that have heretofore 

 been mentioned in this memoir, and also the igneous, were bent and 

 distorted before the great cleavage of the country began ; but the 

 foliation of the rocks of Anglesea was of prior date*. 



It is not intended to be implied in the above remarks that foliation 

 in all cases generally follows the planes of bedding, but only that, if 

 the rocks be uucleaved when metamorphism takes place, the foliation 

 planes will be apt to coincide mth those of bedding ; but, if intense 

 cleavage has occurred, then it may be expected that the planes of 

 foliation vrill lie in the planes of cleavagef. 



Section No. 3. The Longmynd district. — It is foreign to my 

 present purpose to enter on descriptions of the Berwyns. It has 

 been already shown bj^ Professor Sedgwick, and confirmed by the 

 Officers of the Geological Survey, that the Berwyn rocks partly re- 

 present the Bala Series. I may now add, that it seems possible to 

 trace the evidences of both the igneous series of Merionethshire and 

 Caernarvonshire in these rocks. Neither shall I enter on any de- 

 scription of the Caradoc sandstone and Wenlock and Ludlow rocks 

 that run from the neighbourhood of Conway to the country south- 

 west of Builth. The Builth rocks and those of the Shelve country, 

 associated with igneous rocks, are well known, from the descriptions 

 of Sir Roderick Murchison and other authors, to form part of the 

 Llandeilo or Bala group, and there can be no doubt that the Long- 

 mynd rocks bear the same relation to the lowest black slates below 

 the Stiper Stones, that the Barmouth and Harlech grits do to the 

 Lingula flags of Merionethshire. One important result, however, 

 has arisen in the construction of the sections across the Longmynds 

 by Mr. Aveliue, — I allude to the thickness of the strata. 



Between the Church-Stretton valley and the country from half a 



* There is no doubt that m many cases the foliation of the Anglesea rocks runs 

 much across the dip of the' strata. The author hopes to enter on the subject more 

 at large in a subsequent communication. 



t See Ramsay's Geology of Arran, 1841, pp. 88 and 89, where foliation is de- 

 scribed as having taken place approximately in the planes of bedding. The word 

 " foliation," not having been then invented, is not used, but the phsenomenon is 

 described. In 1846 Mr. Darwin, in his ' Geology of South America,' takes notice 

 • of the probability of foliation being found in the general direction of the planes 

 I of bedding and oblique lamination, and minutely and ably desciibes the passage 

 of cleavage into foliation. ' His remarks on this subject form a perfect model of 

 the true mode of investigating the subject. 



It is woi-thy of remark, that the foliation of the schists of Arran took place 

 previously to the deposition of the Old Red Sandstone. The Grampian rocks 

 were also altered before that date, for the Old Red Sandstone contains pebbles of 

 the altered rocks. May it not be that the granites and syenites of these districts 

 are of the same age as those of Wales, viz. of Lower Silurian date .' 



