Geological Society of London. 421 



might be assigned, they were evidently comparatively recent. The phenomena 

 shown in the section described by Mr. Prestwich corresponded with what might 

 be observed in modern beaches. The angular gravels might be due to glacial 

 action. 



Mr. Gv/yn Jeffreys stated that the first shell-sand obtained from the raised beach 

 was found to contain forms identical witli those of the existing beach, but the 

 second collection gave species not found nearer than Scarborough and Dublin. 

 He referred especially to the presence of Cyprina 7ninuta — a Greenland form found 

 on the coasts of New England, rare in the south of England, but common in 

 Shetland. He regarded the raised sea-beach as of the same character as those in 

 Scotland containing a northern fauna ; the species v/ere essentially northern, and 

 no Mediterranean forms were met with. In the Selsea raised beach the species 

 are of southern forms. 



Mr. Prestwich, in reply, stated that the fissures referred to by Mr. Fisher are 

 quite recent, and contain remains of the wild boar. They had nothing to do with 

 the raised beachesw The pebbles he considered to have been transported before 

 the denudation. 



3. " On the Character of the Diamantiferous Kock of South 

 Africa." By Prof. N. Story Maskelyne, F.R,S., P.G.S., Keeper, 

 and Dr. Flight, Senior Assistant, of the Mineralogical Department, 

 British Museum. 



In this paper the authors confirmed certain statements made by 

 one of them from a superficial examination of specimens brought to 

 this country by Mr. Dunn. The specimens examined and analyzed 

 by Dr. Flight were obtained from various diggings and from different 

 depths, down to 180 feet in the case of one mass from Colesberg 

 Kopje. Their characters throughout are essentially the same. 



The rock consists of a soft and somewhat pulverulent ground- 

 mass, composed of a mineral (soapy to the touch) of a light yellowish 

 colour in the upper, and of an olive-green to bluish-grey colour in 

 the lower parts of the excavations. Interspersed in the mass are 

 fragments of more or less altered sh-ale, and a micaceous-looking 

 mineral of the vermiculite group, which sometimes becomes an im- 

 portant constituent of the rock, which also contains bright green 

 crystals of a ferruginous enstatite (bronzite), and sometimes a 

 hornblendic mineral closely resembling sraaragdite. A pale buff 

 bronzite occurs in larger fragments than the green form of the 

 mineral; and in the rock of Du Toit's Fan an altered diallage is 

 present. Opaline silica, in the form of hyalite or of hornstone, is 

 disseminated through the greater pa>rt of the rock-masses, and they 

 are everywhere penetrated by calcite.. 



The analyses of the component minerals (given in detail in the 

 paper) show that this once igneous rock is a bronzite rock converted 

 into a hydrated magnesium silicate, having the chemical characters 

 of a hydra,ted bronzite, except where the remains of crystals have 

 resisted metamorphism. Except in the absence of olivine and the 

 small amount of augitic mineral, it might be compared with the 

 well-known Lehrzolite rock. 



The diamonds are said to occur most plentifully, or almost exclu- 

 sively, in the neighbourhood of dykes of diorite which intersect the 

 hydrated rock, or occur between it and the horizontal strata through 

 which the igneous rocks have been projected. The authors compare 

 the characters of the diamonds found in different position&, and 



