156 



G. T. PEIOB. 



The numbers obtained in the analysis correspond to the 

 following " norm " :— 



28-92 



In the American system of classification the rock would be 

 classed as Toscanose. 



The rhyolitic rocks of the Lebombo Range appear to be of 

 about the same age as the dolerites and basalts, for whereas 

 in one part of the Eange they are said to lie " conformably 

 upon the basaltic series which overlie the coal-bearing Ecca 

 series^' in another part they appear to be cut by dolerite 

 dykes.^ Like the granophyres, they are probably a differ- 

 entiation product of the same magma which supplied the 

 dolerites. Although the microscopic charcters of some of the 

 rocks suggest at first some resemblance to the Kenytes, the 

 analyses show that on the whole the rocks are nearer to the 

 Pacific than to the Atlantic type. 



EXPLANATION OF PLATES III— YI, 



Illustrating Dr. Gr. T. Prior's paper, " Petrographical Notes 

 on the Dolerites and Ehyolites of Natal and Zululand.'' 



PLATE III. 



Fig. 1. — Ophitic dolerite from Ugata Hill, Zulnland (p. 143). Olivine 

 penetrated by and enclosing felspar laths. The felspars are represented 

 as seen between crossed nicols. Magnification 60 diam., 1-in. objective. 



Fig. 2.— Contact-dolerite from Umhlali Beach, Natal (p. 146). 

 Glomero-porphyritic masses of clear glassy felspar in variolitic base. 

 Magnification 60 diam., 1-in. objective. 



^ See Anderson, 'First Repoi-t,' pp. 60, 62, and Kynaston, 'Trans. 

 Geol. Soc. S. Africa,' ix (1906), p. 27. 



