ON ITS EXTERIOE. EARTHQUAKES. 175 



or secondary phenomenon, and not the intensity of the 

 undulation which had traversed a portion of the 

 earth's crust, which would be the true occasion of the 

 gradual, very important, and too little regarded exten- 

 sion of circles of commotion, or earthquake regions. ( 245 ) 

 Manifestations of volcanic activity, to the lower gra- 

 dations of which earthquakes belong, almost always 

 comprise at once phenomena of movement, and physical 

 production of substances. I have already noticed in 

 the Description of Nature in the first volume, how 

 there rise from fissures at a distance from any volcano : 

 water and hot steam ; carbonic acid gas and other 

 suffocating exhalations ; black smoke, (as, for many 

 days, at the rock of Alvidras in the Lisbon earthquake 

 of Nov. 1, 1755); flame, sand, mud, and Moya with 

 intermixed carbonaceous matter. The great geologist 

 Abich has pointed out the connection between the ther- 

 mal springs of Sarcin (about 5382 feet high), in Grhilan 

 in Persia, on the road from Ardebil to Tabreez, and the 

 earthquakes by which those highlands are visited at 

 intervals of two years. In October 1848, an undulatory 

 movement of the ground, which lasted an entire hour, 

 obliged the inhabitants of Ardebil to leave the town, 

 and at the same time the temperature of the springs, 

 which is between 44 and 46 Cent. (111-2 and 114-8 

 Fahr.), rose for a whole month to scalding heat.( 24G ) 

 Perhaps there is no place on the earth where, as Abich 

 has told us, " the intimate connection of earthquakes 

 producing fissures, with the phenomena of mud vol- 

 canoes, salses, inflammable gases permeating through 

 loose soil, and petroleum springs, is more distinctly 

 indicated, and may be more clearly recognised, than at 



