286 ECON^OMIC GEOLOGY. 



ferruginous quartz and three of gravel from the stream flowing at the 

 base of the section exposed were submitted to the gold assay without, 

 however, detecting the slightest trace of that metal. 



Another specimen in Mr. Cruger's possession, given to him as 

 auriferous, and as proceeding from the slate quarry, was a dark green 

 slate, with disseminated pyrites, but quite dissimilar to any of the 

 strata detected in the section at the quarry. On examination it yielded 

 the remarkably insignificant amount of .00009 per cent, of silver, or 

 .03 ounce per ton, containing also a minute quantity of gold. It may 

 be remarked that traces of gold are often present in pyrites, but not 

 to such an extent as to warrant extraction, for which, in the case refer- 

 red to, about 250 tons, the amount indicated, would be requisite. 



QUARTZ VEINS AND MINERAL LODES. 



In reference to quartz veins it may be well to explain that they 

 must be distinguished from mineral veins, or lodes, which are mechan- 

 ical fissures, first open, and afterwards filled with metallic ores and a 

 variety of other minerals. No indication of the existence of such fis- 

 sures has been detected during the geological survey. The former 

 are due to metamorphic action, which has induced the segregation of 

 the excess of quartz into the lines of weakness between the lamina3 of 

 the strata produced by the stratification or cleavage ; the instances of 

 metals or metallic ores associated with these veins are exceptional, 

 although the substance next to be considered affords an illustration 

 of its occurrence, viz : 



IRON. 



The oxide of this metal is intimately mixed with quartz in certain 

 strata of this district, belonging to the mica slate or lowest division, 

 and found especially abundant in the " Quebrada de Hierro." Mag- 

 netic and sjjecular iron ores, free from quartz and containing 60 to 66 

 per cent, of metallic iron are found traversing quartzose slates, and 

 sandstones parallel to the laminar structure, and filling joints, or any 

 minor crevices which may exist. These iron ores are present in con- 

 siderable quantities, and the metal might undoubtedly be produced 

 from them, as the abundance of wood in the vicinity furnishes the 

 charcoal necessary for smelting; it is also probable the iron would be of 

 good quality, but the experience of other countries shows that the seg- 

 regated ores of iron contained in the metamorphic rocks are both ex- 

 pensive in extracting and difficult of reduction to the metallic state. 



Considering these facts in connexion with the high price of skilled 

 labor, and the low price at which imported iron is furnished, it is 

 doubtful whether the attempt to work these deposits would be attended 

 with profit. The ores of iron are found so abundantly in the coun- 

 tries, which are the seats of its m^anufacture, that the expenses of ex- 

 traction and transport would scarcely allow the colonial ores, however 

 rich, to be advantageously exported. The blocks of iron ore found at 

 Gasparilla, though rich, are apparently present to a limited extent 

 only. 



