108 
TfiE GEOLOGIST. 
coast of the Isle of Bourbon. This sand is extremely interesting, first, 
by the great distance whence it has found its way into my laboratory in 
Paris ; secondly, by its composition and aspect ; and, last, perhaps not 
least, from its containing small quantities of gold. Three or four 
analyses made in Paris show that it contains 5 o u o 0 th of its weight of 
gold : it is almost entirely black, of a very fine grain, and, from the slight 
examination I have as yet given it, appears to consist chiefly of nigrine 
(titanate of iron), mixed with grains of quartz, garnets, corundon, &c. 
The nigrine is easily separated from the rest by means of a magnet, for 
this mineral is extremely magnetic. There are a great number of other 
black grains, however, upon which the magnet has no action, and which 
appear to be either debris of basalt rocks or crichtonite.* 
It would certainly be desirable and, perhaps, profitable, were some 
of our English ships touching at the Mauritius to bring back to England 
samples of sand taken from the coasts of the last-named island, whose 
geological structure is identical with that of the Isle of Bourbon,f and 
whose shores are doubtless strewn with a similar auriferous sand. 
Analysis and experiment would soon decide if the washing of this sand 
for its gold would prove a profitable undertaking, and whether we 
should thus be enabled to join to the organic produce of the Mauritius 
a mineral of quite as much importance. Besides the sand of which 
we speak, the ocean throws on to the coasts of the Isle of Bourbon (and 
I have reasons to suppose, on to the coasts of the Mauritius also), round 
blocks of what appears to me to be a species of trap-rock, which also 
contains a notable proportion of gold. 
M. Delesse has lately made knownj the results of his investigations 
on " The Metamorphism of Eocks."§ We extract what appears to us 
most interesting. 
* Another species of titanate of iron, which is not magnetic. 
■j- Both are volcanic islands : their soil is strewn with lava, basalt, &c. Bourbon 
has one volcano still active ; those of Mauritius have long since ceased their 
eruptions. 
J In a series of memoirs, of which extracts have been given in the " Comptea 
Rendus," from September to December, 1857. 
§ Transformed or metamorphic rocks are those in which the internal texture, the 
mode of stratification, and sometimes the chemical composition, have been changed 
either by contact with, proximity to, a plutonic or volcanic rock of eruption. (For 
details on this interesting subject sec Humboldt's " Cosmos," vol. I, p. 248, el scq.) 
