TRANSACTIONS OP THE SECTIONS. 129 



no pebble could have found its way to Haldon. Even if some paroxysm be supposed 

 to have uplifted the gi-anite in a solid state, so as to shiver the overlying- crust and 

 thereby to facilitate the work of denudation, still the time required, even thus, appears 

 to be so very great, so completely overwhelming, so entirely incapable of compres- 

 sion, that it is impossible to regard the red conglomerate as belonging to the Per- 

 mian formation, the representative of the period next succeeding the Carboniferous. 

 Indeed if we conceive of the Dartmoor gTanite being called into existence, as such, 

 at or subsequent to the close of the Carboniferous period, and laid bare prior to the 

 era of the Lower Trias, and that, during the interim, a pile of rocks of considerable 

 thickness, covering an area of 200 square miles, had been stripped off, we get a rough 

 yet oveiii\'helming measure of the chronological interval, the Permian period. 



The facts of the case appear to require the belief — 



1st. That the Dartmoor granite is not older, at most, than the close of the Car- 

 boniferous period. 



2nd. That it was exposed at the earth's smface when the materials of the red 

 conglomerate were being accumidated. 



3rd. That the conglomerates are not of higher antiquity than the Lower Trias. 



4th. That the Permian period was one of gi-eat dm-ation. 



Notice of the Post-glacial G-raveh of the Valley of the Thames. 

 By Professor Phillips. 



On the Gold of North Wales. By T. A. Readwin, F.G.S. 



The author confined his obser^•ations in this paper to an area of about twenty square 

 miles, situated north of the turnpike road leading from Dolgelly to Barmouth. 

 Professor Ramsay has ably described the geology of this disti'ict in a communica- 

 tion to the Geological Society of London in 1854, entitled " The Geology of the 

 Gold-bearing Districts of Merionethshire." The Dolgelly district is bounded by 

 the river Mawddach, the great Merioneth anticlinal range, and the little river 

 Camlan. In this district are found the Cambrians, overlaid by the Lower Silurian 

 Lingular. The Cambrian rocks are coarse greenish-gi-ey grits, and the Lingula-flags 

 are .arenaceous slatj' beds, intersti-atilied with com-ses of s.andstone. Calcareous 

 and greenstone dyke's frequently penetrate both the Cambrian and the Silurian rocks. 

 The metalliferoi{s products are chiefly argentiferous galena, copper pn'ites, blende, 

 manganese, and mimdic, associated fi-equently with gold. According to Sir R. 

 Mmchison, " the most usual position of gold is in quartzose veinstones that traverse 

 altered palaeozoic slates, frequently near their junction with eruptive rocks, whether 

 of igneous or of aqueous origin. The sh-atified rocks of the highest antiquity, such 

 as the oldest gneiss or quartz rocks, have seldom borne gold ; l)ut the sedimentary 

 accumulations which followed, or the Silurian, Devonian, and Carboniferous (parti- 

 cidarly the firet of these three), have been the deposits which, in the tracts where 

 they have undergone a metamorphosis or change of structm-e, by the influence of 

 igneous agency or other causes, have been the chief sources whence gold has been 

 derived." After refen-ing to the opinion of Professor Ramsay that gold in the Ural 

 Mountains, Australia, &c. occurred in rocks of a similar age and character, the 

 author stated that Sir R. Murchison's statement is sing-ularly coiToborated by the 

 position of the quartzose vein in the Clogaii Mine, distinguished as the " Gold Lode," 

 which traverses altered palseozoie slates near the junction of an eruptive bar of 

 poi-phyritic greenstone ; and the same law appears to obtain also with respect to all 

 gold-bearing quartzose veins of the Dolgelly district, upon the ores of which he 

 had made a very large number of experiments during the past eight years. There 

 are in this disti-ict about twenty localities in which gold has been discovered visible 

 in quartz, or associated more or less with galena, blende, copper-pj-rites, telluric 

 bismuth, carbonate of lime, schist, barj-ta, iron-pjTites, &c. By far the richest dis- 

 coveries of gold have been made at the Dol-y-frwj-nog, Prince of Wales, Cambrian, 

 and the Clogau mines. Gold has also been found in the " Marine drift " by the 

 Hon. r.Walpole, Sir Augustus Webster, the author, and others, a piece of which was 

 exhibited. Mr. Arthur Dean, in a paper read before the British Association in 1844, 

 stated that a complete system of auriferous veins exists throughout the whole of 

 the Snowdonian or Lower Silmian formations of North Wales. Upon the feith of 



1861. 9 



