244 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 1, 



slaty beds of the Lingula-flags (No. 2) traversed by greenstone dykes 

 (No. 5) on the hills immediately N. of Pigswch. They are suc- 

 ceeded by a mass of intrusive greenstone (No. 5'), which is bounded 

 on the N. hy an E. and W. fault and lode on the N. part of Moel- 

 Hafod-Owen. From this point the greenstone passes S., with two 

 interruptions, by Tyn-y-Ben-rhos to Moel Cynwch, about two miles 

 further S. E. of this greenstone are a set of rocks (No. 3), which 

 possess a very peculiar lithological character, and which occur very 

 sparingly elsewhere, either among the Lingula-flags or in any other 

 geological area in Wales. It is in a lode traversing this "country" 

 that the most important of the gold discoveries has lately been made. 

 The rock commences at what may be called the S.W. angle of Moel- 

 Hafod-Owen, above Buarth. The same E. and W. fault that bounds 

 the greenstone, limits it on the N. Aline of fault drawn southward from 

 thence to where the brooks join, nearly opposite Dolau, forms its east- 

 ern boundary so far. From thence the Afon-wen forms its boundary 

 for nearly a mile and a half S. It is not improbable that this may also 

 be a continuation of the same line of fault. The boundary-line then 

 crosses the stream, and still passes southward to the ground that lies be- 

 tween Cefn-mawr and the precipitous rocks that overhang the ]\Iaw- 

 ddach above Dol-y-clochydd. The rock itself is one of those problem- 

 atical masses to which it is difficult to give a definite name. In some 

 places it is so hard and massive, that a hand-specimen is difficult to 

 distinguish from some of the felspathic traps of the neighbouring 

 country. Even then, however, it is more or less flaky, and constantly 

 passes into a talcose rock, which in places at the surface and in the 

 lodes decomposes into a kind of talcose unctuous clay. In many 

 places it graduates in the line of strike into ordinary slaty rocks, which 

 then become largely interstratified with it. As it passes southwards it 

 becomes more and more slaty and sandy, and passes by degrees into 

 rocks possessing all the characters of the Lingula-flags of the district. 

 On the E. it is bounded by slaty Lingula-flags (No. 4), on which 

 rests the massive greenstone mass of Rhobell-fawr (No. 5"). The ordi- 

 nary Lingula-beds spread far to the northward, by Ffestiniog, towards 

 the southern slopes of the Manods and the Moelwyns. They are slaty 

 and sandy by turns. Several lodes occur in this country in the neigh- 

 bourhood of Dol-y-frwynog and Cwm Eisen. The gold at Cwm 

 Eisen was discovered in 1 843, by Mr. Arthur Dean, who, in a paper 

 published in the Report of the British Association for 1844, also 

 stated " that a complete system of auriferous veins exists throughout 

 the whole of the Snowdonian or Lower Silurian formations of North 

 Wales." Recent events would seem, in a slight degree, to verify this 

 bold assertion ; but from that date to this time no one has heretofore 

 attempted to work any mines in North Wales for gold, except that 

 at Cwm Eisen ; nor have I ever met with any miner who has seen 

 any gold of the alleged auriferous veins, with many of which I am 

 also well acquainted . Cwm Eisen has been several times worked ; but, 

 I believe, never with a steady profit. The gold is found in a branching 

 lode containing lead. Its principal branch runs north-easterly, and is 

 mostly composed of exceedingly hard quartz, which crosses the river 



