Investigations and Writings of Baron Humboldt. 217 
wich islands, with the mountain of Mowna Roa, which has a 
height of 15,000 feet. 
These remarkable facts, by which our geognostical know- 
ledge has been so essentially enriched, are related, along with 
a multitude of detailed observations, in Humboldt’s Travels 
in the equinoctial regions of the New Continent (Rezsen in die 
Aequinoktial gegenden des neuen Kontinentes), in 4 volumes,” 
and the Essai Politique sur la nouvelle Espagne, 4 volumes, 
2d edition, 1825. The description of the rocks of America, 
and their comparison with those of Europe, are contained in 
the more general work, Essai Géognostique sur le Gisement 
des Roches dans les deux Hémisphéres, 1823.+ In this last 
work there is given a very complete general view of the 
known mountain rocks, with full information on the literature 
of the subject. Directly connected with this work is an essay, 
rich in clear views on the structure and action of volcanos, 
read to the Academy of Sciences of Berlin, on the 24th of 
January 1823. 
In later times, Humboldt has not ceased devoting himself 
_ with zeal to the objects of our science. His journey to Asiatic 
Russia, undertaken in 1829, and which extended to the fron- 
tiers of China, has produced important results for the exten- 
sion of our geognostical knowledge. One of the objects of 
this journey was to obtain more accurate information respect- 
ing the constitution of the metallic repositories of the Ural, 
and more especially to compare with analogous phenomena in 
America the characters of the alluvial matters containing 
gold and platina, which had been recently met with covering 
a large extent of country on both sides of that chain. 
He found in this respect a remarkable agreement ; for both 
in the Ural and on the west side of the Cordilleras of South 
America, the gold and platina are separated precisely in a 
similar manner in repositories quite distinct from each other. 
The auriferous alluvial matters presented themselves together, 
and with extremely trifling exceptions, in a district extending 
along the east side of the Ural; they there include an extent 
* Translated into English by Helen Maria Williams. 
t Translated into German by C. yon Leonhard ; and into English, 1823. 
