578 Geological Society, 



the centre (as it might do, had the earth, originally cold, been as Pois- 

 son supposes, kept for a few billions or trillions of years in a firma- 

 ment full of burning suns, besetting every outlet of heat, and then 

 launched into our cooler milky-way) ; still as all we want is no more 

 than a heat sufficient to melt silex, &c., I do not think we need 

 trouble ourselves with any inquiries of the sort, but take it for granted 

 that a very moderate plunge downwards in proportion to the earth's 

 radius, will do all we want*." 



A paper was next read, entitled " Description of the Insulated 

 masses of Silver found in the mines of Huantaxaya, in the province 

 of Tarapaca, Peru ;" by Mr. BoUaert, and communicated by Mr. 

 Darwin, F.G.S. 



The mines of Huantaxaya are three leagues from the Port of Iqui- 

 qui (lat. 21*> 13' S. long. 70« W.), and in a mountain-hollow 2800 

 feet above the level of the sea. This depression is bounded towards 

 the west by a hill called Huantaxaya, 3000 feet above the sea level, or 

 200 feet above the hollow, and on the opposite side by a hill of si- 

 milar height. The great mass of the mountain consists of a reddish, 

 argillaceous limestone, but the escarpment, towards Iquiqui is co- 

 vered with loose sand, and near the base, porphyiy and granite are 

 visible. ^JThe limestone is traversed by numerous argentiferous and 

 other veins, which range fromN.E. by E., to S.W. by W., but the 

 mines of Huantaxaya are in a superficial detritus called Panizo. 



This deposit is from eighty to one hundred yards thick, and is 

 composed of fragments of limestone not water- worn, and dried mud 

 apparently derived from the same rock. It is divided into beds, 

 some of which, called Sinta,are metalliferous, and others, called Bruto, 

 are barren. The nodules of ore, to which the name of papa has 

 been applied, from their resembling a potatoe in form, consist of 

 pure silver, chloride, and other chemical compounds of silver, sul- 

 phurets of copper and lead, and carbonates of copper. The papas 

 are of all sizes, and some have produced 160 ounces of pure silver in 

 a hundred pounds. One celebrated papa weighed about 900 pounds, 

 and resembled in shape the top of a table. The miners believe, that 

 each layer of Sinta has been derived from a particular vein in the 

 limestone, and that they can determine to which vein a papa origin- 

 ally belonged. 



The only instruments used in working the Panizo, are an iron bar 

 six inches long and a small iron mallet. With these tools, the Pa- 

 nizero rapidly advances in the soft materials, but rarely makes 

 a larger excavation than is sufficient for his body to pass on hands 

 and knees. In clearing out the contents of these honey-combed 

 galleries, a hide-bag is strapped over the shoulders and under the 

 arms; but in crawling through the narrower parts, the miner trans- 

 fers the bag to one of his feet and drags it after him. 



The danger of working these unconsolidated beds is greatly en- 

 hanced by frequent shoclfs of earthquakes. 



• [See the President's Address, and also the Proceedings of the Royal 

 Institution, p. 519 and 533 of our last number.] 



