220 REACTION OF THE INTEEIOR OF THE EARTH 



period of my visit pieces of sulphur were only found 

 from 6J to 8J inches in size; pieces of three or four 

 feet had been found earlier. Even a spring of naphtha 

 may be actually seen to rise from mica-schist at the 

 bottom of the sea in the Grulf of Cariaco, near Cumana. 

 The naphtha gives a yellow colour to the surface of the 

 sea for a distance of more than 1000 feet, and I found 

 its smell diffused so far as the interior of the peninsula 

 pf Araya. ( 304 ) 



If we now cast a last glance on that kind of volcanic 

 activity which manifests itself by the emission of vapours 

 and gases, either with or without igneous phsenomena, 

 we find sometimes great affinity, and sometimes an 

 equally remarkable diversity, in the escaping substances, 

 according as the high internal temperature has exerted 

 its modifying influence on the mutual action either of 

 homogeneous or of highly diversified materials. The 

 substances which this low degree of volcanic activity 

 brings to the surface are aqueous vapour or steam in 

 large quantities, chloride of sodium, sulphur, carburetted 

 and sulphuretted hydrogen, carbonic acid and nitrogen, 

 naphtha (colourless, yellow, or as brown petroleum), 

 boracic acid gas, and clay of the mud-volcanoes. The 

 great diversity of these substances, of which some, how- 

 ever (common salt, sulphuretted hydrogen, and petro- 

 leum), are almost always associated together, shows the 

 inappropriateness of the term " salse," derived from 

 Italy, where Spallanzani had the great merit of first 

 directing the attention of geologists to the previously dis- 

 regarded phenomena of this kind in the territory of Mo- 

 dena. The terms "gas-springs" and "vapour-springs" 

 are more generally expressive. While doubtless many 



