PKOCEEDIXGS OF THE GEOLOGICAL SOCIETY . 7 



The following communications were read : — 



1. " The Boulder-Clays of Lincolnshire : their Greographical Eange 

 and Eelative Age." By A. J. Jukes-Browne, Esq., B.A., F.G.S. 



2. " On the Geology of the Eio-Tinto Mines, with some general 

 remarks on the Pyritic Eegion of the Sierra Morena." By J. H. 

 Collins, Esq., E.G.S. 



3. " On some new or imperfectly known Madreporaria from the 

 Great Oolite of the Counties of Oxford, Gloucester, and Somerset." 

 By E. E. Tomes, Esq., E.G.S. 



Specimens of Elint implements were exhibited by John Evans, 

 Esq., LL.D., E.E.S., E.G.S. 



Eebruary 11, 1885. 



Prof. T. G. BoOTTEY, D.Sc, LL.D., E.E.S., President, in the Chair. 



Arthur "William Clayden, Esq., M.A., I^orth Lodge, Bath College, 

 Bath; Samuel Eideal, Esq., B.Sc. (Lond.), E.C.S., Devon Lodge, 

 Mayow Eoad, Forest Fill, S.E. ; and H. W. Williams, Esq., Solva, 

 Pembrokeshire, were elected Eellows of the Society. 



The List of Donations to the Library was read. 



The following communications were read : — 



1. "The Tertiary and Older Peridotites of Scotland." By Prof. 

 John W. Judd, E.E.S., Sec.G.S. 



2. " Boulders wedged in the Ealls of the Cynfael, Ffestiniog," 

 By T. Mellard Eeade, Esq., E.G.S. 



[Abstract.] 



This paper briefly described certain phenomena of stream-denu- 

 dation observed in the bed of the Cynfael, which has cut a deep 

 channel through the Lingula Flags, the course of the channel being 

 mainly dependent on the jointing of the rock. In one spot the 

 upper beds at the top of the gorge have slid upon the lower along 

 their dip, about 10° to north by east, so as to project over the 

 stream like a corbel ; and advantage has been taken of this to form 

 a bridge by means of a slab of rock laid from the projecting mass to 

 the top of the opposite bank. At another point several very large 



