198 TRANSACTIONS OF SECTION C. 



The general character of the diamantiferous gravel, and the concentrates 

 therefrom, occurring at the site of the first discovery, suggests a derivation 

 from a granite-pegmatite area, but the angular quartz and the ragged gold are 

 undoubtedly of local origin. Since veins of quartz occur plentifully in the 

 underlying rocks, this angular material has most probably been derived there- 

 from. The diamond found at a depth of about eight feet in the Birrim terrace 

 gravels, and those found in the streams to the north-west and the north-east, 

 show clearly that some at least of the stones, though detrital, are not of local 

 derivation. 



The matrix of the diamonds has not yet been determined. The stones may 

 have been derived from volcanic pipes of kimberlite, as in South Africa, or of 

 dolerite, as in New South Wales, intruded into or through the Birrim series in 

 Birrimian (pre-Cambrian ?) or post-Birrimian times ; or from conglomerates 

 of those times ; or they may have been formed by the action of pegmatite dykes 

 or granite intrusions on carbonaceous rocks of the Birrim series. Whatever 

 may be the origin of the stones, the evidence so far obtained suggests that they 

 have not been derived directly from pipes, but that they are detrital. 



In the afternoon a Sectional Excursion to Barton and Hordle Cliff took 

 place. 



SATVIWAY, SEPTEMBER 13. 

 Sectional Excursion to Lulworth. 



SUNDAY, SEPTEMBER 14. 

 Sectional Excursion to Kimmeridge. 



