108 



THE 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 wir-roth 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 

 (tifcanate 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 dehris 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 mads kQown| the results of his investigations 

 on " The Metamorphism of Rocks."§ We extract what appears to us 

 most interesting. 



Another species of titanate of iron, which is not magnetic, 

 t 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. 



t In a series of memoirs, of which extracts have been given in the " Comptes 

 Rcndus," 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 

 cither by contact with, proximity to, a plutonic or volcanic rock of eruption. (For 

 details on this interesting subject see Humboldt's " Cosmos," vol. I, p. 248, et seq.) 



