INTRODUCTION. 65 



gestive ideas which were not without their influence in directing 

 subsequent investigation to the causes of great cliraatological 

 variations. 



Humboldt, who was in possession of large private means, 

 now began to make arrangements for a few years of travel on a 

 large scale, and went in May 1798 to Paris. In June 1799, 

 accompanied by the botanist Aime Bonpland, he set out for 

 Central and South America. 



The expedition was undertaken primarily to obtain more 

 knowledge of the physical geography and botany of tropical 

 regions, but Humboldt at the same time devoted a large share 

 of attention to the volcanoes, earthquakes, and geological struc- 

 ture of the New Continent. He said that one of the chief 

 motives of his journey was to test a hypothesis which he had 

 formed that the older strata composing mountain-systems 

 had a parallel strike. It had struck him during his stay in 

 the Fichtel mountains that the older members in the rock- 

 succession showed always a N.E.-S.W. strike; and he found 

 the same general strike in the Erz mountains, the Salzburg 

 Alps, and the "slate" mountains of the Rhine. He had 

 therefore concluded that all the older rock-formations of the 

 earth strike in N.E.-S.W. direction, and cross the meridians at 

 a constant angle of about 52. 



His observations in Columbia and in the coastal ranges of 

 the Gulf of Mexico led to the same result, and from this agree- 

 ment he drew the general principle that the strike of the older 

 strata was quite independent of the geographical trend of 

 mountain-systems, and was regulated by a force which took its 

 origin in the original laws of attraction governing terrestrial 

 matter. This principle has, however, proved quite untenable, 

 and is at the present day completely forgotten. 



After a short stay in Teneriffe, Humboldt landed at Vene- 

 zuela, and in November 1799 for the first time witnessed an 

 earthquake at Cumana. He made a detailed study of 

 Venezuela, then spent some time in the Orinoco district, and 

 was in Cuba from December 1800 until March 1801. After- 

 wards he proceeded to New Granada, Peru, and Ecuador, 

 where he remained until 1803, then worked for a year in 

 Central America. In the summer of 1804 he returned by 

 Havana and North America to Paris. There he became at 

 once absorbed in physical and chemical studies, conducted 

 along with Biot, Gay Lussac, and Arago, and he also com- 



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