68 
HINTS TO TRAVELLERS. 
A collection of rock specimens may show what kinds of rock occur in a 
country, but the information afforded is very meagre, and, in general, of 
very small value. Such collections, indeed, unless made by a geologist, 
and accompanied by notes, are scarcely worth the carriage. If such 
specimens are taken, care should be used to select them from the rocks 
in place, not from loose blocks that may have been transported from a 
distance, and no fragments of spar or crystals should be collected merely 
because they are pretty. 
In taking specimens of useful minerals, such as coal or metallic ores, 
the traveller should always endeavour to procure them himself from 
the place of occurrence, and if such are brought to him by natives, he 
should, if practicable, visit the locality whence the samples were pro¬ 
cured. The value of all useful minerals depends both on quality and 
quantity; the former can to some extent be ascertained from a sample, 
but the amount available can only be estimated after a visit to the locality. 
Most metallic ores occur in veins or lodes. These were originally cracks 
in the rock, and have been irregularly filled with minerals, different from 
those in the neighbourhood. It is, however, very difficult, and often 
impossible, to estimate from surface examination whether the quantity 
of ore occurring in veins is likely to prove large; some idea may possibly 
be obtained if underground workings exist. Many of the ores of iron, 
some of those of other metals, and all coal and salt occur in beds, and 
here it is important to see what is the thickness, and to ascertain whether 
the mineral is equally pure throughout. Iron ores occur in most 
countries, and unless very pure and within easy reach of water-carriage, 
are not likely to be worth transport. The value of salt also depends on 
facilities for carriage. Coal, however, may be of value anywhere; but it 
is improbable that seams of less thickness than four or five feet can be 
of much use, except in countries where there is a skilled mining popula¬ 
tion and a considerable demand for the mineral. It does not follow 
because much thinner seams are sufficiently valuable to be worked in 
Western Europe that they would pay for extraction in a country where 
the mechanical arts are less advanced. Still the occurrence of thin seams 
is worthy of record, as thicker deposits may exist in the neighbourhood. 
It must not be inferred, however, that a seam of small thickness at the 
surface will become thicker below. The reverse is equally probable. 
A blow-pipe is extremely useful for ascertaining the nature of ores, and 
