44 Report S.A.A. Advancement of Science. 



A large group of minerals, the Zeolites, hydrated Silicates, are 

 well represented in South Africa. Of great beauty and variety are 

 especially the Apophyllites, Natrolites and Mesotypes, Prehnites, 

 from Kimberley, Jagersfontein, Beaufort West, and Cradock. They 

 furnish splendid material also to the physicist, who investigates the 

 optical properties of these minerals. They were specially valued by 

 the famous Descloisaux, Professor of Mineralogy in Paris, who 

 studied principally the physical properties of these Zeolites. But I 

 know that there are found at some places, for example, near Hope- 

 town, on the Orange River, Zeolites, that is to say, hydrated silicates 

 of secondary formation, which are new, and not investigated yet. 

 Beautiful specimens for the study of the paragenesis of Quartz and 

 Prehnite are furnished by the Prehnites of Beaufort West and 

 Cradock. These Zeolites are found and observed in the vicinity 

 of the Dolerite, Uiorite, Melaphyre dykes and intrusions which 

 traverse the geological formation of South Africa from Simon's 

 Town to the Zambesi. A close and detailed study and investigations 

 of these interesting and beautiful minerals here in South Africa will 

 not only throw much light on the formation of these minerals, but 

 will also lead to the discovery of new, hitherto unknown, represent- 

 atives of this group of minerals. ' The effect of the climatic con- 

 ditions upon the disintegration of minerals and rocks and the 

 secondary products formed in this disintegration is also a subject of 

 great scientific interest. In many localities in the Karroo are found 

 pebbles of ferruginous clay, which are surrounded by a coating of 

 Magnetic Oxide of Iron, which is undoubtedly formed under the 

 influence of the hot and dry state of the air of the Karroo during a 

 considerable part of the year. Another problem which calls for 

 investigation are the products of the disentegration of Doleritic and 

 Basaltic rocks. At some localities, for example, near Colesberg, the 

 Dolerite hills are white, as if they had been whitewashed from the 

 Carbonate of Lime formed in the decomposition of the rock ; at 

 other localities the same rock has put on a protecting coat of Oxide 

 of Iron, and at others it crumbles to a sandy powder, yielding a dark 

 red-brown soil. Also the oil shales between Kimberley and Boshof 

 are not investigated yet as to their nature and commercial value. 

 Equally interesting for scientific investigations are the Quartz crystals 

 found near Carnarvon, containing cavities partly filled with oil — 

 rock oil ; also the rock in which these crystals occur contains rock 

 oil. Now there is a great difference between Hydrocarbons making 

 up the American rock oil and those of the oil from Baku on the 

 Caspian. It would be of great scientific interest to know what the 

 composition and constitution of the oil is which has been found at 

 certain localities here in South Africa. 



There is one more subject I should like to draw your attention 

 to, although many others could be mentioned. In some of the caves 

 on the coast near Saldanha Bay is found a peculiar deposit 

 of Phosphate of Lime, closely resembling the Phosphorites of Spain 

 and the hard Sambrero guano. This is evidently formed of the 

 guano of seal)irds. It is quite a unique formation, a fossilized guano. 



