422 
THE VOYAGE OF THE VEGA. 
[chap. 
weathered constituents have been for the most part changed 
into a fine mud, and as such washed away, while the hard gems 
have only been inconsiderably rounded and little diminished in 
size.' The current of water therefore has not been able to wash 
them far away from the place where they were originally im¬ 
bedded in the rock, and we now find them collected in the 
gravel-bed, resting for the most part on the fundamental rock 
which the stream has left behind, and which afterwards, when 
the water has changed its course, has been again covered by 
new layers of mud, clay, and sand. It is this gravel-bed which 
the natives call nellan, and from which they chiefly get their 
treasures of precious stones.^ 
Of all the kinds of stones which are used as ornaments there 
are both noble and common varieties, without there being any 
perceptible difference in their chemical composition. The most 
skilful chemist would thus have difficulty in finding in their 
chemical composition the least difference between corundum and 
sapphire or ruby, between common beryl and emerald, between 
the precious and the common topaz, between the hyacinth and 
the common zircon, between precious and common spinel; and 
every mineralogist knows that there are innumerable inter¬ 
mediate stages between these minerals which are so dissimilar 
though absolutely identical in composition. This gave the old 
naturalists occasion to speak of ripe and unripe precious stones. 
They said that in order to ripen precious stones the heat of the 
south was required. This transference of well-known circum¬ 
stances from the vegetable to the mineral kingdom is certainly 
without justification. It points however to a remarkable and 
hitherto unexplained circumstance, namely, that the occurrence 
of precious stones is, with few exceptions, confined to southern 
regions.^ Diamonds are found in noteworthy number only in 
^ The only considerable exceptions from this are two localities for pre¬ 
cious stones in Southern Siberia and the occurrence of precious opal in 
