492 '/. Allan Thomson — Diamond Matrices of Australia. 



The photograph reproduced with this paper will convey a good idea 

 of the flat ground occupied by the moraine-matter ; the bailey-castle- 

 crowned tump of Silurian rocks on the north side of the Edw Gorge, 

 and the steep, wooded Aberedw rocks on the south side. 



The material of which the moraine-deposit that occupies the mouth 

 of the Aberedw Valley and stretches some way up the valley eastwards 

 is composed is excellently exposed in a pit close by the Wye and in 

 the lane-sides near the village school. Well-smoothed boulders of 

 diabase - porphyrite and andesite from the craggy Carneddau and of 

 Caban conglomerate from the neighbourhood of Rhayader are easily 

 identifiable rocks amid the preponderating element of fissile and less- 

 travelled slabs of Wenlock and Ludlow rocks. Small fragments and 

 large are confusedly intermixed in characteristically morainic fashion 

 in a matrix of finer material. 



Moral Tie 



Pre ^"^\ '^^"'"^/^'^^ ^^^^ 



Post Glaaal^^__W^i^^^^ castle- 



courses ^~~TbmfH^xe,dv^<^^o^"^^ 

 of the ^ W 

 Edw f^L^er ^ /i i 



of the ^ W'i ,p,,^L. ^ craq. 

 Gra vel-fi i r ^ f^ou Iwau. 



Fig. 1. Diagrammatic sketch of the country around Aberedw, near Builth Wells. 



All down the Wye Valley between Aberedw and Boughrood well- 

 defined patches of gravel form interrupted terraces, but at Boughrood 

 there is a considerable spread rendered all the more apparent by an 

 extensive pit at Boughrood Station. The railway traverses this bank 

 of gravel and negotiates it by means of a steep gradient between the 

 station and the Wye bridge, while the Wye escapes between the 

 gravel patch and the steep western valley side, subsequently proceeding 

 to describe the most noticeable horseshoe bend that there is in many 

 miles of its course. Probably this gravel-deposit is one of several 

 terminal moraines that mark the recession of the Wye Glacier. 



The valley and tributary combs of the Upper Wye are rich in the 

 products of the ice-action of the Glacial Epoch, and it is hoped that 

 the phenomena described in the present paper will lend stimulus to 

 their systematic investigation, which should result in the piecing 

 together of a chapter of Glacial History no less instructive and 

 valuable than that contributed by those who have studied the glacial 

 phenomena of the Yorkshire moors. 



VI. — The Diamond Matrices of Australia. 

 By J. Allan Thomson, B.A. (Oxon), B.Sc. (N.Z.), A.O.S.M., F.G.S. 



SINCE the exhibition of the diamond in a dolerite at York and 

 Mexico by Professor Edgeworth David, great interest has been 

 aroused in the Copeton occurrence. Specimens of the rock and 



