308 PEOCEBDINGS OF THE GEOLOGICAL SOCIETY. [April 24, 



ming's reef," however, parallel conditions occur, and several hun- 

 dred tons of rock were crushed with remunerative results, until the 



Fig. 17. — Section in Tunnel Claim, " Upper Cape Diggings'' 



A. Mica and hornblende schists. 



B. Dyke of felspar porphyry cutting the schists nearly at right 



angles to their dip. 



C. Dyke of felsite mined for gold. 



water-level was reached, when the necessity for a supply of expen- 

 sive pj.impiug machinery checked the enterprise for a time. 



The analysis of the auriferous matrix of Cumming's Eeef afforded 

 me: — 



Silica 69-900 



Alumina 12-737 



Ferric oxide 4-413 



Oxide of copper 1-875 



Magnesia 0-130 



Potash 0-600 



Soda 6-539 



Loss at red heat 3-500 



99-694 



The analysis agrees with the examination under the microscope, 

 which indicates its approximate composition to be : — 



Per cent. 



Quartz 10-000 



Triclinic felspar 80-000 



Decomposed pyritous element 10-000 



The iron and copper are produced by the decomposition of pyrites, 

 the iron being chiefly in the form of brown iron-ore, and the copper 

 occurring as silicate. A little titanic acid and manganese were 

 found, but not quantitatively ascertained, the object of the examina- 

 tion being to determine the alkalies, and so approximately the 

 felspar element. 



This so-caUed " reef" is 10 feet wide where worked; and the 

 walls are composed of micaceous diorite. A nearly parallel case is 

 mentioned by the geologist of Southern Queensland as occurring at 

 Ban Ban, in the Gayndah district. He says, " There is no appear- 

 ance of a mineral lode or vein of any kind on the spot. The mate- 

 rial, of which three tons were sent to the Sydney Mint for assay, 

 which resulted in a return of one ounce six dwts. of gold per ton, 

 was taken from a mass of partially decomposed felspar porphyry, 



