﻿part 3] 



VOLCANIC HOCKS OF MOZAMBIQUE. 



279 



the Author, that alkaline and non-alkaline rocks were to be found 

 along the African coast in intimate association. It was not 

 clear, however, from what had been said, on what principle the 

 Author separated the rocks that he put into his alkaline group 

 from the others with which he had dealt, and it was not easy 

 to see why they should be treated apart. It was interesting to 

 note that, although alkaline volcanic rocks were so often found in 

 the coastal regions, there were no occurrences known in the inland 

 districts of this part of Africa. 



Dr. J. W. Evaxs congratulated the Author on his presentation 

 of the results of several years' work on some very interesting 

 rocks. He had not confined himself to simple descriptions of 

 structures and minerals, but had endeavoured to ascertain what 

 light the facts disclosed threw on the evolution of igneous rocks, 

 especially those rich in alkalies. The speaker enquired whether 

 there was any evidence that the alkali-rocks were later than those 

 of normal types in this area. 



Mr. A. E. Kixsox congratulated the Author on the paper. He 

 asked whether there was any general linear arrangement of the 

 dykes, and if so, whether the lines were parallel with the coast. 

 He said that on both sides of Africa, wherever late volcanic rocks 

 occurred, it seemed that they had been extruded along lines of 

 fracture roughly parallel with the coast, or in fracture-zones 

 inland, and that on the Gold Coast volcanic necks and plugs 

 occurred in several places along the Volta River ; but he had not 

 found similar evidence in that colony outside of zones of fracture. 



The AriHOE, in reply, thanked the Fellows for their kind 

 reception of his paper, and stated that most of the points raised 

 in the discussion were f>iHy dealt with in the paper itself. 

 Answering Mr. MennelL he said that the division of the lavas 

 into- tun series__3Eag^pased on analyses, variation-diagrams, the 

 composition of the amygdale-minerals, and in part on the sequence, 

 so far as this was known. In reply to Dr. Evans, he was sorry to say 

 that there was no definite field-evidence from which the relations 

 of the two series could be deduced. Referring to Mr. Kitson's 

 remarks, he observed that, as in many other of the African coast- 

 lands, the main faidts were parallel to the prevailing trend of the 

 coast, and most of the basaltic dykes followed the same direction. 



