192 REVIEWS 
series is intruded by a great variety of porphyritic rocks and is overlaid by 
sandstones and conglomerates forming a series from 2,000 to 3,000 feet 
thick, which is in the main flat lying and is not greatly deformed. This 
group of rocks is not known to contain fossils, but its relationship to rocks 
of known age is said to have been made out in Venezuela where it is regarded 
as Cretaceous. The schists and the sandstones are intruded by diabase 
which the author regards as a source of much of the gold. The relatively 
fresh rock carries from a trace to 17 grains per ton. 
Owing to the humid climate and tropical vegetation the rocks have 
weathered to great depth. Laterite, the residual product of the basic rocks, 
is known to be as much as roo feet deep in some places. In the laterite there 
isa marked concentration of iron and clay and locally of gold, which it carries 
in amounts varying from traces to 15 pennyweights per ton. ‘The laterite 
also contains irregular masses of rich quartzose ore which is presumably 
altered vein-stuff, but such masses are not abundant and the conclusion 
is that not more than ro per cent. of the placers have originated from 
quartzose ores. The principal source is regarded as the basic igneous 
rocks in which, through decomposition to laterite, there has been a marked 
concentration im situ. Further concentration has taken place in some 
of the stream gravels. From the descriptions given, the laterite areas seem 
to offer attractive fields for prospecting for large low-grade gold deposits 
which should be very economically worked. 
The World’s Gold. By L. DE Launay, with an Introduction by C. 
A. Conant. Translated by ORLANDO CypRIAN WILLIAMS. New 
York and London: G. P. Putnam’s Sons. 
This work is arranged for the banker and economist, rather than the 
geologist and metallurgist. The geographic distribution and the extraction 
of gold are treated in an interesting and readable manner, but the future 
production of gold is obviously the subject which is of greatest importance. 
Statistics are given which show that the gold production of the world has 
steadily increased since the Boer war, reaching over four hundred million 
dollars in 1906. The writer concludes that the next fifteen years will prob- 
ably be marked by a great production of gold, which will afterward decline. 
He concludes, however, that the supply will be adequate for the purposes 
required, owing to a more general use of instruments of credit. 
