374 DOMAIN XII. VOLCANIC. 



and even of Vesuvius. Yet no writer has men- 

 tioned with precision what form this mud as- 

 sumes after desiccation. Brochant indeed, who 

 has borrowed his arrangement of the volcanic 

 rocks from Dolomieu, supposes that they be- 

 come volcanic tufo*. But this substance is ge- 

 nerally understood to be formed of volcanic sand 

 and powders, dross, pumice, and pulverised 

 lava. The grand volcanoes of Cotopacsi, Tun- 

 garunga, and San gay, in South America, eject 

 prodigious quantities of mud ; and, what is still 

 more striking, vast numbers of fish, so as some- 

 times to infect the air with putrefaction. These 

 fish appear to be little injured, and are the same 

 with those found in the rivulets at the bottom of 

 the volcanoes, being aptmelodes silurus, from two 

 to four inches in length ; but they are very rare 

 in the rivulets which they probably remount, in 

 order to pass to subterranean lakes, and are 

 caught by the natives at the very sources ; facts 

 which tend to confirm the theory of volcanoes 

 above hinted. 



Late writers specially mention that the muddy 

 eruptions become fertile clay, and are very pro- 

 ductive; while tufo can never be regarded as a 

 productive soil. If the muddy eruptions be 



* This is the Italian and classical orthography. Tufa may be 

 reserved for depositions merely aqueous. 



