I 



456 A CONTRIBUTION TO THE GEOLOGY OF VITI LEVU, FIJI, 



series, obtained just north of Nasava, as a fine quartzite. It and 

 its associates, extending from Nasava to Narokorokoyawa, are 

 very strongly cleaved, and are, to all appearance macroscopically, 

 slates. My suspicions were aroused on finding that some of the 

 rocks contained porphyritic felspar, and I made an extensive 

 collection in this locality. Microscopic examination of a large 

 number of sections* show that, while many of the rocks vary 

 between actinolitic quartzite and actinolite schist, others are 

 apparently trachytic in structure and composition. Most of 

 these trachytic rocks are strongly silicified and saussuritized, and 

 nearly all show traces of strain. I have etched and stained all 

 the more likely looking ones, but have been unable to detect any 

 nepheline. 



It is probable that these rocks represent, not highly altered 

 sediments, as I formerly thought, but highly metamorphosed 

 trachytic lavas and possibly tuffs. While this is so, the possi- 

 bility of some sediments being present is not excluded. 



This discovery very seriously weakens my previous con- 

 clusions as to the great age of the slaty rocks, since it shows that 

 the entire absence of fossils is not due to high antiquity and 

 extensive metamorphism. Nevertheless I claim that all the 

 evidences point to a considerable age for these rocks. They are 

 unconformably overlain b}^ andesitic lavas and tuffs, which liave 

 none of the signs of chemical and mechanical alteration so con- 

 spicuous in them. They are associated with granitic rocks 

 of coarse grain, and have strain-structures analogous to those 

 found in the granites. The extreme complexity of their jointing 

 proves that they have been subjected to several distinct earth- 

 movements in different directions. 



Mawson's discover}^ of jointed Miocene tuffsf in the New 

 Hebrides at least suggests the possibility of a similar age for 

 these rocks. The analogy must not, however, be strained too 

 far; he found no trace of granites, while, in Fiji, these cover 

 enormous areas. 



* To be described in a subsequent paper, 

 t These Proceedings, 1905, Vol.xxx. p.446. 



