3 902.] NATURAL SCIENCES OF PHILADELPHIA, 747 



the Eocene ocean, where this foraminifer dwelt, just as the dredg- 

 ings of the Challenger and other deep sea explorers have 

 found it in the oceans of to-day. This resulted in the formation 

 of a manganiferous Eocene limestone, which tropical conditions 

 have largely removed as soluble bicarbonate of caicium, concen- 

 trating the binoxide of manganese as the present pyrolusite ore 

 deposit. 



In 1524 the copper mines of the Sierra Cobre were opened. 

 As high as fifty tons of ore a day have been mined from them, 

 and the shafts are said to extend vertically for twelve hundred 

 feet. The breaking out of the ' ' Ten Years' War ' ' put an end 

 to the Avorking. From 1867 to 1901 nothing was done. The 

 workings are said to be the largest in the world. This is to-day 

 indicated only by the himdreds of tons of ruined machinery, huge 

 buildings and dumps with innumerable abandoned shafts and 

 tunnels. Owing to the dilapidated and extensive nature of the 

 Cobre deposits, a detailed study of them was impossible. The 

 principal copperiferous ,veins seem to perpendicularly cut, a shale 

 whose dip is 70°, strike S. 20° W, Of course many offshoots 

 occur, adding to the complexity. The ore at present mined and 

 shipped seems to be an intimate mixture of oxide, carbonate and 

 silicate of copper. Sulphides exist further down as they were 

 found in the old dumps. Azurite and chalcopyrite were found in 

 place. Oxide of iron, pyrite, crystals of quartz of peculiar habit, 

 oxide of copper and other minerals forming a gossan, are met 

 with, but not in good specimens. The water now filling the mines 

 is highly charged with chalcanthite and melanterite, rude plants 

 are in operation removing the copper from solution, Chalcanthite 

 and brochautite are often found deposited in unexposed places. 



A mile or so upstream from the village, on the Rio Cobre, there 

 is an interesting mineral occurrence. Here a pyritiferous dike or 

 vein cuts a calcareous rock. The pyrite is oxidized to sulphate of 

 iron and the iron precipitated as hydroxide by vegetable matter, 

 producing in the reaction sulphuric acid. This in acting on the 

 calcium compounds has produced gypsum. The gypsum thus 

 formed is not crystallized in the usual shapes, but by a multiple 

 growth along certain axis, produces unusual forms and combina- 

 tions. In many instances the crystalline masses are of limpid 

 pureness, free from inclusions. Again the molecules in their 

 arrangement seem to include as much foreign matter as possible. 



In the valley of the San Juan, near the hill famous in history, 

 which is a coarse conglomerate gravel, are deposits of clay which 

 yield a rather inferior brick. Here are also deposits of sand and 

 gravel extending to a considerable depth, as the experimental wells 

 put down by Mr. LaBelle preliminary to operations on the new 

 Santiago waterworks indicated. This sand and gravel is mostly 

 too coarse for building. The valley of the San Juan was evidently 



