TRANSACTIONS OF THE SECTIONS. 73 



its peculiar fossils, including several species of insects, and of the Limulus or 

 King Crab, I must refer them to Prestwich and Hull, and the Memoirs of the 

 Ordnance Survey. 



On the Recent Discovery of Gold at Gwynfynydd, North Wales. 

 By T. A. Bead win. 



Notes on the Theory of Repidsion as illustrative of Physical Geology pro- 

 pounded by Dr. Winslow of Boston. By George E. Eoberts. 



On a Fossil Sjrider lately discovered in the Coal-measures of Upper Silesia 

 (Prussia). By Professor Eerd. Eoemer, of Breslau. 



The author exhibited the specimen itself to the Section. It lies extended on the 

 surface of a piece of coal-shale, and is beautifully preserved. Besides the outline 

 of the body, it shows distinctly the four pairs of legs, and the two palps with their 

 articulations. Even the coriaceous integument of the body, and the hairs attached 

 to the legs are preserved. The interest of the discovery of this spider lies in the 

 fact, that hitherto spiders were not known from any rocks older than the Jurassic, 

 and that now their existence in the Pala?ozoic rocks is proved. From the resem- 

 blance to the recent genus Lijcosa, and its occurrence in the Coal-measures, the 

 name of Protohjcosa anthracophihi was proposed for the species. 



On a Coal Field in Brazil. By G. E. Eumney. 



Explanation of a Map of the Faults in the Gold District of Dolyclly. 



By J. W. Salter. 

 The district examined during the autumn of 1864 included the greater portion 

 of the right bank of the Mawddach river, from the waterfalls above Dolgelly to the 

 Clogau Gold Mines nearer Barmouth, and advantage was taken of the dry weather 

 in September and October to search the watercourses for evidence of the faults 

 which cut up the mining region. Particular attention was paid to the portion 

 about the waterfalls, and a few miles south. The results showed that while the 

 major lines of fault ranged with the strike around the nucleus of Lower Cambrian 

 rocks, and repeated the beds, thus widening the area of the Lower Lingula Hags, 

 the other faults, which are very numerous, and have not yet been shown on any 

 map, are reducible to three or four series, the order being as follows : — 



1. A series of east and west faults (Clogau, Gwynfynydd, &c.) of small amount, 

 bearing quartz lodes and visible gold, copper blende, galena, iron, arsenic ; these 

 are crossed by — 



2. Faults, rarely of large amount, about 30° or 40° north of east, occasionally, as 

 at Cefn Coch (Welsh gold mines), rich in the precious metal, but also as at Cwm- 

 heisian lead mine, with lead, or at other places copper, &c. 



The above two series may be of one age ; and are certainly the oldest. They 

 have reference probably to the first undulations of the North Welsh district, and 

 which run in a north-east and south-west direction. 



3. Strike faults, following the outline of the Lower Cambrian nucleus (the 

 Merioneth anticlinal of Professor Sedgwick), and hence varying in direction, more 

 northerly on the upper waters of the Mawddach, more easterly along the estuary. 

 Parallel faults to these occur in the great porphyry range of Arran, and of Cader 

 Idris, and are marked on the Survey map. 



4. North-west and south-east faults, of no great amount, usually as copper or 

 lead lodes, but often bearing gold, (Tyddyngwladis silver lead mine and Dolfrwynog 

 gold mines are examples). They are numerous, and as yet only known near the 

 waterfalls, and thence to Dolfrwynog. 



5. A grand series of north and south faults, usually 15° to 18° west of north, 

 which cross and interrupt all the foregoing series, shifting the lodes and cross courses 

 and giving the features to the ground throughout the whole of the gold mining 

 districts. These are traceable by cliffs and ravines, river and brook courses, ledges 



