40 Puqjorts tC' Proceedings — Cambridge Phil. Society. 



I?,E!I=OI?.TS .A.lSriD :E=E,OCElE:iDI3Sr<3-S. 



I. — The Cambkidge Philosophical Society. 



On a remakkable instance of complete Bock Disintegkation by 

 Weathering. Abstract of a paper read by Dr. F. H. Hatch before 

 the Cambridge Philosopliical Society on November 25, 1912. 



rpHE material described comes from Diamantina, in the province of 

 J_ Minas Geraes, Brazil, where it is being worked for diamonds. 

 It occurs as a loose sandy deposit in which there are a number of 

 partially disintegrated pebbles, and is sufficiently soft to be dug out 

 Avith the shovel at the lowest depth yet attained in the open- wot king. 



Tlie pebbles consist of quartzite, vein-quartz, steatite, and tourma- 

 line-quartz vein-stuff. The sand is a mixture of colourless quartz 

 and of the fine powder produced by the pulverization of the steatite 

 fragments. The lieavy minerals in the residue obtained by treatment 

 with bromoform, are the following: zircon, zinc blende, galena, iron 

 ])yrites, chiilcopyrite, rutile, and tourmaline. 



The material has evidently resulted from the prolonged weathering 

 of an ancient conglomerate formation. The weathering agents have 

 not only removed the cement of the conglomerate, but have also 

 abstracted the material that originally cemented the constituents of 

 the quartzite pebbles, which have consequently been reduced to 

 a friable condition, and can even be crushed to powder between the 

 finjicrs. 



The diamonds, which occur in the following forms — octahedron, 

 rhombic dodecahedron, three-faced octahedron, and six-faced octa- 

 liedron, have a characteristic greenish tint, seen under the microscope 

 to be due to the presence of small spots and flecks of some chloritic 

 mineral. It is, however, only ' skin-deep ', the cut stones being 

 perfectly clear and colourless. 



II. — Geological Society of London. 



Novetnher 20, 1912. — Dr. Aubrey Strahan, F.B.S., President, 

 in the Chair, 



The following communications were read : — 



1. "On the Hafslo Lake and the Solvorn Yalley (Norway)." By 

 Horace Woollaston Monckton, Treas.L.S., F.G.S. 



The district dealt with lies north of the main Sogne Fjord and 

 west of tlie Lyster Fjord. Attention is drawn to a series of valleys 

 running from the area of the Jostedal snowfield and cutting the belt 

 of Silurian rocks which crosses the disti'ict in a north-easterly and 

 south-westerly direction, and to a second series of valleys which run 

 parallel to the snowfield and to the Silurian belt. The author traces 

 the valley of the Vejtestrands Lake, which belongs to the first of 

 the above series, until it reaches the Hafslo Lake, which lies at 

 a point where the valleys of the two series intersect. The present 

 line of drainage follows a valley of the second series from tlie lake 

 to the fjord, but a disused outlet from the lake to the fjord is 

 described belonging to the first series. The author, while thinking 



