216 REACTION OF THE INTERIOR OP THE EARTH 



upheaved in the form of a small sandy island, which, 

 however, disappeared again soon afterwards. More than 

 fifty " volcancitos " (cones similar to those of Turbaco) 

 now surround (in some cases at a distance of sixteen or 

 twenty miles) the submarine gas-volcano of the Galera 

 Zamba. This may well be regarded as, in geological 

 respects, the principal seat of the volcanic activity 

 which throughout the low-lying district of Turbaco, 

 and extending over the delta of the Eio Grande de la 

 Magdalena, strives to place itself in contact with the 

 atmosphere. 



The similarity of the phenomena shown, in the dif- 

 ferent stages of their activity, by the salses, mud-vol- 

 canoes, and gas-springs on the Italian peninsula, in the 

 Caucasus, and in South America, is displayed over vast 

 tracts of country in the Chinese empire. There the art 

 of man has, since very early times, utilised these great 

 natural supplies; and for this object had arrived long 

 since at the very ingenious invention with which Euro- 

 peans only became acquainted at a far later period, 

 that of " Chinese rope-boring." These borings, several 

 thousand feet deep, were effected by the simplest ap- 

 plication of man's bodily power, or rather of his weight. 

 I have elsewhere ( 298 ) treated in detail of this invention, 

 as well as of the " fire-springs " (Ho-tsing), and of the 

 fire-mountains (Ho-schan), of Eastern Asia. Men bore 

 for water, salt, and combustible gas, from the south^ 

 west provinces of Yun-nan, Kuang-si, and Szu-tchuan 

 on the borders of Thibet, to the northern province of 

 Schan-si. The gas burns with a reddish flame and often 

 diffuses a bituminous smell : it is conveyed to a distance, 

 sometimes through pipes of bamboo, sometimes in port- 



