Vol. II, part 2, issued December 20th, 1910. 



DOLERITES AND RHYOLITES OF NATAL AND ZULULAND. 141 



Petrographical Notes on the Dolerites and 

 Rhyolites of Natal and Zululand. 



By 



Ci. T. Piior, i?I..4., D.Sc, F.G.S., 

 Keeper of Minerals in the British Museum. 



With Plates III-VI. 



The following petrographical notes are the result of an 

 examination of a large number of rock specimens, which were 

 collected by Mr. W. Anderson when acting as Government 

 Geologist of Natal during the years 1899-1905. The speci- 

 mens are mainly of igneous rocks, which are briefly referred 

 to in the three Reports of the Geological Survey of Natal and 

 Zululand published in 1901, 1904, and 1907 respectively, 

 under ]Mr. Anderson's direction. Small fraofments, too^ether 

 with thin slices of the rocks were placed at my disposal for 

 examination by Dr. E, Warren, Director of the Natal Govern- 

 ment Museiim at Pietermaritzburg ; and the following brief 

 notes, the result of that examination, are here placed on 

 record, since they present some points of interest, although 

 unfortunately they cannot be accompanied by any very 

 detailed descriptions of the mode of occurrence of the rocks 

 in the field. 



Most of the specimens are of the dolerites which occur so 

 ubiquitously as intrusive dykes and sills in the Karoo forma- 

 tion of South Africa, but the collection also includes rhyolitic 



VOL. 2, PART 2. 11 



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