MIXING ASD AGRICULTURE. 405 



the preliminary researches. At the present time it is not 

 precious metals solely which should fix the attention of 

 new mining companies ; the multiplication of steam-engines 

 renders it indispensable, wherever wood is not abundant or 

 easy of transport, to seek at the same time to discover coal 

 ana lignites. In this point of view, the precise knowledge 

 of the red sandstone, coal-sandstone, quadersandstein, and 

 molassus (tertiary formation of lignites), often covered with 

 basalt and dolerite, is of great practical importance. It is 

 difficult for a European miner, recently arrived, to judge of 

 a country presenting so novel an aspect, and when the same 

 formations cover an immense extent. I hope that the 

 present work, as well as my Political Essay on New Spain, 

 and my work on the Position of Bocks in the Two Hemi- 

 spheres, will contribute to diminish those obstacles. They 

 may be said to contain the earliest geologic information 

 respecting places whose subterraneous wealth attracts the 

 attention of commercial nations; and they will assist in the 

 classification of the more precise notions which later re- 

 searches may add to my labours. 



The republic of Colombia, in its present limits, furnishes a 

 vast field for the enterprizing spirit of the miner. Gold, 

 platinum, silver, mercury, copper, gem-salt, sulphur, and alum, 

 may become objects of important workings. The production 

 of gold alone amounted, before the outbreak of the political 

 dissensions, on the average, to 4700 kilogrammes (20,500 

 marks of Castile) per annum. This is nearly half the 

 quantity furnished by all Spanish America, a quantity which 

 has an influence the more powerful on the variable propor- 

 tions between the value of gold and silver, as the extraction 

 of the former metal has diminished at Brazil, for forty 

 years past, with surprising rapidity. The quint (a tax which 

 the government raises on gold- washings), and which in the 

 Capitania of Minas Geraes, was, in 1756, 1761, and 1767, 

 from 118, 102, and 85 o.robas of gold (of 14-J- kilogrammes), 

 has fallen, during 1800, 1813, and 1818, to 30, 20, and 9 

 arobas ; an arob of gold having, at Eio Janeiro, the value of 

 15,000 cruzados. According to these estimates, the produce 

 oi gold in Brazil, making deductions for fraudulent exporta- 

 ation, was, in the middle ot the eighteenth century, thd 

 years of the greatest prosperity of the gold- washings, 0600 



