from the Observations of himself and Mr. Clemson. 21 



solute barrenness and redundant fertility, is not the least strik- 

 ing among the peculiarities of the region under consideration. 

 We have chosen here to advert to it, because it cannot fail to 

 be seen from this circumstance, that in an ceconomical point of 

 view it bears materially upon the convenience, and conse- 

 quently upon the local value, of sites hereafter designed to be 

 scenes of a busy population connected with the mines, which 

 though seated within an area of positive sterility will derive 

 incalculable benefits from their proximity to one of the utmost 

 fecundity. 



flocks of the Savanas. — Our notice of the rocks and nature 

 of the ores of this region will be brief, and will be reserved 

 in detail for another place. The rocks of the mineral district 

 may be divided into two classes: those which contain much 

 diallage and are more or less crystalline in their structure; 

 and those in which that mineral is wanting or is less prevalent; 

 and they all may be arranged under the head of serpentine 

 rocks. 



They are sometimes distinct, and, again, are mixed in all 

 proportions. The surface rock, as well as that which has 

 been extracted from the shafts and levels but which has been 

 exposed for a while, is more or less in a disintegrated form ; 

 of a soft unctuous touch, and easily reduced to powder. As 

 the constituents of this rock happen to vary, it changes into 

 one of a petrosiliceous nature, is hard, and resists the disin- 

 tegrating nature of the atmospheric agents. We have pre- 

 viously made mention of this class of rocks in our account of the 

 bituminous veins within them, in the vicinity of the Havana*. 



Copper Ores. — The surface ore, or the mineral substance 

 containing copper, that is found at the outcrops, or upon the 

 back of the veins within a few feet of the surface of the ground, 

 differs materially in its physical characters and in its chemical 

 composition from that ore which is found to predominate in 

 the same lode at greater depths. The term surface ore is here 

 applied to amorphous or informal masses of mineral, of dif- 

 ferent colours, containing more or less metallic matter. 



Frequently at the outcrop of veins containing cupriferous 

 ores, the term surface ore is applied to a heterogeneous mix- 

 ture of several distinct mineral species, of which copper forms 

 one of the constituents, associated with other minerals of little 

 or no value. These ores are generally red, brown, black, 

 green, and the different hues that grow out of an indiscri- 

 minate mixture of those colours ; the most prominent of these 

 species being the oxides, sulphurets, silicates, and caibonates 

 of copper, with iron, &c. As we descend upon the vein the 



* Set Loud, and Edinb. Phil. Mag., vol. x. p. 161.— Edit. 



