288 ADDENDUM. 



obtained. At the bottom of the valley a hole eighteen to twenty feet deep has been excavated by 

 Indians, who expected to encounter a vein of iron ; and at several directions from this principal 

 one, at distances of ten to twenty steps, there are other apertures and piles of rubbish two to 

 three feet high, indicating, beyond doubt, the places from which the largest and heaviest pieces 

 of this greatly-sought substance had been extracted. At Atacama I heard it said that there 

 was still a large mass buried in the surface, and one Manuel Plaza told me, at Peine, that a 

 very great specimen was rolled to the bottom of the valley; but I saw nothing of either. I 

 remember reading, in a manual of mineralogy, that a stone weighing three hundred pounds 

 had been obtained from here ; but it must be a mistake, because masses of that weight cannot 

 be carried by mules, and they afford the only mode of transport on the desert. 



Arriving at the spot, we began the search for specimens. Nothing was found at the bottom 

 of the valley or on the northern slope ; but, in a search of more than an hour on the southern 

 declivity, and at an elevation of seventeen to twenty-eight feet above the bottom of the valley, I 

 found a very great number of small fragments, within a space from sixty to eighty steps long 

 by twenty paces broad. 



The surface has been formed from the decomposition of certain clasfses of porphyritic rocks, 

 and is composed of a loose clayey earth mixed with an infinity of little stones, from the size of 

 a walnut to that of an apple, and does not differ essentially from the greater portion of the 

 desert. The porphyry may be termed granitic or sienitic, because, in a whitish, crystalline, 

 felspathic component, of which the oxide of iron on the surface becomes reddish, we find dis- 

 seminated grains of hyaline quartz, slightly inclined to gray, which are of the size of hemp- 

 seed. Small black spots, more or less dendritic, appear to arise from manganese; but in some 

 cases they are jjositively known to be amphibole, as in a specimen I have marked A. It is very 

 rare to find, as in one marked B, any specimens containing small spots of white mica, which 

 forms the transition to granite, and are more granular. Some of these stones have their sur- 

 faces covered with a black rust, which appears to be principally formed of the hydrated oxide 

 of iron, as in the specimen marked C. The most remarkable thing is^ that all of them have 

 their angles very sharp, proving that they have not been rolled from afar, but were formed on 

 the same spot by natural fracture of the rock. 



The specimens I collected weigh three pounds, less three drachms, and number 673; so that 

 the mean weight of each is twenty-three grains — the largest weighing two ounces, and the 

 smallest one less than one grain. We may suppose that my companion, Don Guillermo Doll, 

 obtained the same number, Jose Maria Chaile as many, and it is probable that one half 

 remained unseen. Therefore the total number of pieces in that locality exceeded 3,000, without 

 enumerating the many large stones carried away during the last thirty or forty years, and 

 which there is no possible mode of estimating. 



The smallest specimens have the forms of lamellas. Among the larger of them there are 

 many of arborescent lamellar forms, with intersecting lines as on paper that has been compressed 

 in the hand and opened again. The surfaces of these are very black, and when collected some 

 of them were iridescent. In their cavities transparent olivine is very distinctly seen, although 

 it is full of crevices, and the hollows are somewhat regular as if the iron had introduced itself 

 when in a state of fusion among already formed crystals of olivine. There are other pieces 

 more compact. The olivine which we must sujipose originally filled their cavities is generally 

 very much decomposed and converted into a whitish-yellow^ or a ruddy and earthy substance 

 whose examination under a lens shows it to be composed of small vitreous or crystalline grains. 

 It would be tedious to describe the varied and multitudinous forms of the Atacama iron ; and 

 the samples that I have the honor to present will save me the irksome task. I must mention, 

 however, the largest specimen seen, and which is in the collection of our colleague Don Ignacio 

 Domeyko. This mass weighs more than fifty pounds, and is of an irregular oblong form with 

 somewhat smooth surfaces and sharp corners. Its smooth sides look as though they had been 

 rubbed down, whilst its elongated extremities are rough and crooked, with indices of octahe- 



