part 1] AND ASSOCIATED ROCKS OF MOZAMBIQUE. 87 



on the exactness of this correlation, for two sets of analyses are 

 but a slender support for so far-reaching a conclusion. The results 

 are placed on record, however, as an example of the method and its 

 application. 



(2) Correlation of the Granulitic Granites. 



Zircons were collected from the granites of the Nrassi Basin, 

 and from those in the neighbourhood of Mpera, Monapo River. 

 These give lead-ratios of 0*17 and 0*15 respectively. Analysis of 

 a biotite (rich in pleochroic haloes), from a similar granite occur- 

 ring near Fort Ligonia, Ligonia River (Zambesia), gives a ratio of 

 0T4. 1 From their structures, mineral composition, and relations 

 to the older rocks, these granites were considered to belong to the 

 same* period of intrusion. The radioactive evidence confirms this 

 view as well as could be expected. Considering the minuteness of 

 the quantities analysed, and the possibility of traces of both 

 original and thorium-lead being present, the three ratios seem 

 sufficiently close to warrant a provisional correlation of the parent 

 rocks from which the minerals were obtained. 



For comparison, an analysis of a Middle Pre- Cambrian uraninite 

 from the Villeneuve Mine, Ontario, is cited in Table XI (p. 86). 

 I am indebted to the Canadian Geological Survey for permission to 

 quote the following information concerning the geological relation- 

 ships of the pegmatite in which the uraninite occurs. The details 

 given below are based on the field-work of Mr. M. E. Wilson. 



' The Villeneuve pegmatite is an elliptical mass, 200 feet long- and 100 feet 

 wide, exposed on the southern margin of a small knob of bedrock protruding 

 through Champlain marine clay. 



' With regard to its age, it is known that it intrudes into garnet-gneiss and 

 vitreous quartz -rock (generally called quartzite) belonging to the Grenville 

 Series, and is, in turn, intruded into by later Pre-Cambrian diabase dykes 

 which are approximately of Keweenawan age. This is all that can be deter- 

 mined from the relationship of the mass itself ; but, from the relationships of 

 similar masses of pegmatite occurring in the district, it is probable that it has 

 been derived from a hornblende-biotite-granite, which occurs in its vicinity as 

 bosses intruding into both the Grenville and the Buckingham Series. 2 It is, 

 of course, impossible to correlate these rocks with Dr. Lawson's Algoman, 

 Avhich occurs over 1000 miles away. Since, however, it is the youngest member 

 of the basal complex, or Laurentian of Logan, as that part of the Pre-Cambrian 

 is represented in the Ottawa district, it is probably late Archaean.' 



We may next turn to some corresponding rocks in the Gaya 

 ilistriet of India, which also contain uraninite. Through the 

 courtesy of Messrs. Martin & Co., the Geological Survey of India 

 obtained a good specimen of uraninite from the Singar Mine, 

 Gaya District, which they kindly sent to me for investigation. 

 In addition to expressing my thanks to the Survey for this valuable 



1 Attempts were made to utilize other biotites, but the association Avith 

 them of autunite completely vitiated the results. 



3 Summary Rep. Geol. Surv. Canada for 1913 (1914) p. 199. 



