MINING AND AGniCULTUKE. 
405 
the preliminary researches. At the present time it is not 
precions metals solely which should, fix the attention of 
new mining companies j 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 
and lignites. In this point of view, the precise knowledge 
of the red sandstone, coal-sandstone, quadersandstein, and 
niolassus (tertiary formation of lignites), often covered with 
basalt and dolerite, is of great practical importance. It is 
dillicult 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 tipain, 
and my work on the Position of Eocks in the Two Hemi- 
spheres, will contribute to diminish those obstacles. They 
may be said to contain the earliest geologic information 
respectin'’' 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 mav add to my labours. _ 
The republic of Colombia, in its present limits, furnishes a 
vast field tor 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 jiropor- 
tions between the value of gold and silver, as the e.xtraction 
of the former metal has diminished at Brazil, for lorty 
years past, with surprising rapidity. The quint (a tax which 
the government raises on gold-washings), and which in tlm 
Capitania of Minas Geraes, was, in 175(3, 1/01, and 1767, 
from 118, 102, and 85 arobas of gold (of 14f kilogrammes), 
has fallen, during 1800, 1813, and 1818, to 30, 20, and 9 
arobas ; an arob of gold having, at Eio Janeiro, t he value of 
15,000 cruzados. According to these estimates, the produce 
of gold in Brazil, making deductions lor fraudulent exporta- 
atiou, was, in the middle of the eighteenth century, 
years of the greatest prosperity of the gold-washmgs, 
