The hookworm disease is very prevalent, but its ravages are not so apparent as in certain other tropical countries. Venereal diseases are exceedingly common. Evidences of the presence of leprosy and elephantiasis are occasionally seen. The measures taken for the segregation of lepers are far from thorough; the lepers' asylum of Santo Domingo City is situated inside the city walls and is surrounded by habitations of the poor. Cases of typhoid fever are sometimes registered during the hot spell, from July to October, but the victims are usually foreigners who have been careless of climatic requirements. The foreigner who will observe temperance and prudence in all things, who will be careful of what he eats and drinks, who will avoid exposure to rain showers, or to drafts when in perspiration, will easily become acclimated. Realizing that many tropical disorders originate in a foul stomach, the natives upon the slightest provocation have recourse to a purgative, and the custom is one which the stranger should not hesitate to adopt. CHAPTER IX GEOLOGY AND MINERALS Rock formation.--Mineral deposits.--Gold.--Copper.--Iron.-Coal.--Silver.--Salt--Building stone.--Petroleum.--Mineral springs.--Earthquakes. The geological formation and the mineral wealth of the Dominican Republic have never been thoroughly studied, in part because of the physical difficulties and in part as a result of the civil dissensions. The government has never had money to spare for such objects, and private investigators have suffered much hardship and lost many days in opening paths through tangled underbrush, and in crossing rugged mountain ranges in uninhabited regions. The physical obstacles and the necessarily superficial examination consequent thereon may explain the contradictions of detail in different reports. About the middle of the nineteenth century several studies were published, and three scientists who accompanied the American Commission of Inquiry in the year 1871 made a report on geological conditions.