Rocks and Minerals of British Guiana. 39 



are found over the surface of the granite in considerable 

 layers, and underlying the gneiss. The composition of 

 the rocks of this group is very variable, the quartz-por- 

 phyry passing into granite on the one hand, and into 

 porphyritic felstone and true felstone on the other. Iron- 

 pyrites often occur in association with them. 



Granite is of very common occurrence as a surface 

 rock throughout the interior of the colony ; and it lies 

 at the base of all the rocks of the country. Its texture, 

 colour, and composition are extremely variable, and in 

 many parts the quartz ranges from the transparent and 

 white varieties to a beautiful opalaceous variety. It is 

 very largely quarried for road-making ; but, as orna- 

 mental stones, the members of this group of rocks are 

 particularly suitable, more especially the granites with 

 opalaceous quartz. 



Such, in the main, may be advanced as a very brief 

 recapitulation of some of the chief and more generally 

 interesting and useful matter, bearing on the rocks and 

 minerals, to be found in these valuable reports — reports, 

 however, which, on account of the extreme difficulty of 

 the investigations made, sadly require extension in order 

 to place the colony under the class of districts to be 

 considered as geologically known. Persons specially 

 interested in the subject should consult the reports for 

 themselves. 



Within the last two or three years considerable attention 

 has been given to the search for gold, and the metal has 

 become, as judged by its export value, the basis of the 

 second industry of the colony — an export second only to 

 theprodufrs of the sugar industry, sugar, rum, and molasses 

 — and if the advance that has been so far made in the 



