356 F. P. Menndl — South African Petrography. 



certain theories in vogue, a complete geology of the Pyrenees has 

 been developed, to which no Pyrenean geologist can contribute 

 without abandoning those habits of cautious statement which are 

 essential to the integrity of his work. 



Note. — Since the above was posted, in January last, the points 

 described have been largely discussed in Parisian publications. It 

 is admitted that the granite, ophite, and supposed Trias are above 

 and not beneath the Cretaceous. It is hence assumed that they 

 must he abnormally carted caps of those ancient formations. The 

 entire evidence of their age being admittedly false, that age is 

 maintained by a paradox that contradicts every detail of the district. 

 There could be no shadow of doubt that they are beneath the 

 Cenomanien, were it not that they are frankly eruptive, and at 

 Salies, as at a hundred other points, flanked by lentiles of eruptive 

 breccia intercalated in the Cretaceous Flysch. In the Alps, the 

 abnormal carting of the Breche du Chablais is similarly assumed, 

 to save the assumption that its volcanic vents are Triassic by 

 micrographic theory. M. Marcel Bertrand regarding the Alps, and 

 M. Haug regarding the Pyrenees, have propounded theories before 

 visiting either chain. Since first exploring the rocks of Salies with 

 the assistance of Leymerie in 1866, I have endeavoured to sacrifice 

 all theory to observation. Unless practical geologists cease to 

 despise controversy, they will find, like myself, that any mention 

 of their work is an outrage, and that any field survey is intolerable 

 polemics. The entire geology of Asia having been yesterday re- 

 formed from Vienna, similar treatment of Alps and Pyrenees 

 is inevitable. It is easier to silence all local observation than to 

 repeat its task. 



V. — CONTKIBUTIONS TO SoUTH AFRICAN PeTROGKAPHT. 



By F. p. Mennell, F.G.S., Curator of the Eliodesia Museum, Bulawayo. 



IT is remarkable, considering the enormous development of igneous 

 rocks in South Africa, that so little has been written concerning 

 the features they present in the field or under the microscope. Eight 

 away from Cape Town into the tropics, plutonic masses, dykes, and 

 lava-flows interrupt the continuity of the sedimentary deposits with 

 astonishing frequency. Some of these rocks, like the Cape Town 

 granite and dolerite, are probably of pre-Silurian age ; ^ others, like 

 the Kimberley lavas, were erupted during the Secondary period ; 

 while others, again, like the dykes and lavas of the Zambesi Valley, 

 are probably of late Tertiary or even geologically recent date, as 

 evidenced by the numerous geysers and hot springs - which repre- 

 sent the final phase of not long antecedent volcanic activity, Thej^ 

 appear to bear the same relation to the volcanoes of Central Africa 

 as the British Tertiai-y lavas do to those of Iceland. 



' They are overlaiu uucouformably by a thick formation which is itself older than 

 the earliest fossiliferous beds (Devonian) of South Africa. 



2 See Ferguson on the geysers of *he Zambesi and Kaful Valleys, Proc. Ehodesia 

 Sci. Assoc, 1902. 



