TRANSACTIONS OF SOCIETIES. 355 



Tn most groups of animals such facts would perhaps imply that 

 the genus had gradually spread from some centre of origin, and 

 had differentiated into several species as it dispersed ; but in the 

 case of such a cavernicolous creature as Eitcrangonyx it is diffi- 

 cult to understand how dis]:)ersal could take place, excepting 

 tluMugli a contiinious s}'stem of subterranean passages. ^Nlr. 

 Metlnien thinks it probable that this is a case of convergent 

 e\"olution. and that, originally a normal fresh-water shrimp, it 

 has gradually acquired a likeness to the other species of Eucran- 

 (/ony.v, as it adopted the cavernicolous habit. To explain the 

 total disappearance of any descendant of the original gammarid 

 stock in our surface fresh-waters, he ]:)oints to the prevalence of 

 fresh-water crabs and prawns in South Africa, and it certainly ■ 

 is a fact that the river crabs are most exclusive creatures, and 

 in many parts of the world prove more than a match for crayfish. 

 In this connection it would be interesting to know what is the 

 evideiice with regard to the antiquity of the fluviatile crabs and 

 other crustaceans in South Africa. Mr. Alethuen now states 

 that he has found another amphipod in the Transvaal : it does 

 not belong to the same family as the Encrangonyx Though we 

 are fairly well acquainted with the couimoner crustaceans of our 

 vleis and streams, these discoveries are enough to show that our 

 knowledge thereon is far from complete. It is especially desir- 

 able that the cave faunas throughout South Africa should be 

 thoroughly explored. 



TRAXS.\CTrOXS OF SOCIETIES. 



Geological Society of South Africa. — Monday, February 12th : Mr. 

 H. S. Harger, President, in the chair. — " Note on the nature and origin 

 of the Vredehoek tin deposits. Cape Town " ; E. H. Nellmapius. The 

 occurrence of primary tin is confined to rocks of the Mahneslniry series. 

 consisting of slates and hard quartzites, situated on the lower slopes ot 

 Devil's Peak, overlooking the city of Cape Town. The tin-bearing zone 

 is 27 feet wide, strikes approximately north and south, and a similar 

 deposit is being prospected on the other side of Table Valley. A very 

 pure cassiterite, reddish or light brown in colour, and sometimes trans- 

 lucent, occurs, in large well-formed crystals, in the veins consisting of 

 large interlocking white quartz grains. The vein quartz shows under the 

 microscope numerous liquid inclusions generally containing gas bubbles 

 The Malmesbury beds were partly shattered by eruptive action, and 

 rendered permeable to the residual waters of the granite, which is in 

 trusive'in the Malmesbury slates: as it is recognised that tin oxide can 

 be carried and deposited by aqueous solutions, even at ordinary tempera 

 tures, it_ seems probable that the mineralisation is due to deposition from 

 magmatic waters or from aqueous solutions whose tin contents have 

 been derived from the underlying granite. 



Chemical. Met.\llurgical, and Mining Society of South Africa — 

 Saturday, February 17th: Mr. C. B. Saner, M.I.M.M., M.I.M.E., Presi- 

 dent, in the chair. — Presidential address : C. B. Saner. Some of the 

 important problems of recent date in connection witli Rand mining were 

 briefly referred to, including the equipment of shafts abo\c and below 



