"The weight of rock and earth becomes too great for the timbers along the sides and across the roof, and they are crushed and broken. But before falling they groan and crack and settle, but rarely give way suddenly. The Indians can tell from long experience when there is any real danger, and are generally quick enough to escape." From mining the conversation turned to general subjects relating to Bolivia. The substance of what the youths learned may be set down as follows: Silver is found in many parts of the republic, and some of the mines are said to yield ore as rich as of Potosi. The Potosi mines are mainly in a single mountain, which has been pierced with more than five thousand tunnels and openings. Gold is found in many places, but it has not been extensively mined. Occasionally large nuggets or masses of pure gold are found, and they bring a higher price as curiosities than when reduced to bullion. One of these masses was detached from a mountain by a stroke of lightning, and sold at an enormous price to the royal museum at Madrid. There are some valuable mines of tin and copper in Bolivia; the tin mines of Oruro are said to be the richest in the world, and copper is said to be as abundant in the mountains of Corocoro as silver is at Potosi. The other mineral wealth of Bolivia is well known, but none of it is available on account of the lack of transportation. The country has no outlet by which it can reach the markets of the world. Transportation to the Pacific coast is over the passes of the Andes and across deserts, while the ocean ports are lacking in facilities for landing or discharging cargoes. There is a route through Buenos Ayres, and another through Brazil; both are long and expensive, and the greater part of the products of the country will not bear the cost of removal. There will be occasion for referring to this subject again. [Illustration: WILD INDIAN OF BOLIVIA.] Bolivia has a little more than two millions of inhabitants, about one fourth of them whites. There are several varieties of the native and mixed races, from the civilized Indians of La Paz and other cities to the wild tribes of the upper waters of the Amazon. The latter lead a wandering life, and wear no clothes; they have resisted all attempts to civilize them, and until recently they were hostile to the white people who passed along the river in boats. A curious story is told of the incident by which their hostility was suppressed. In a survey made by the Bolivian government of the falls of the Madeira River a camp was established on the banks of that stream. Soon after it was located one of the men of the exploring party was taken ill, and his disease proved to be small-pox. He was immediately isolated from the rest of the camp, and carefully attended by the doctor.