a Theory of the Earth. zSl 



fearches : whether they hold in folution earths not ufually 

 foluble in water *. 



B. Obfervations to he made at all Thnes on Volcanoes 

 decidedly J'uch. 



19. Nature of the countries and mountains between which 

 they are found. 



20. Hiftory of the volcano : its form, height, and extent 

 in the moft ancient times j its fucceflive changes down to 

 the prefent moment j its lateral mouths, and the epochs of 

 their formation. 



21. Chronology and enumeration of its different erup- 

 tions ; defcription of them, and their moft remarkable cha- 

 radlers. 



22. Todefcend, ifpoflible, into the craters of extino-uiflied 

 volcanoes ; to meafure their depth ; defcnbe their form, the 

 nature of their fides, their ftrata, and the concretions ad- 

 hering to them, fuch as fulphur, fait, &c. 



22. A. To obferve the /z/OTaro/^5, or jets of fmoke, often 

 acid, which arife; their temperature, their nature, and their 

 efFefts on the lava with which they come in contact. 



23. To examine the fifTures ; whether they contain me- 

 tallic or ftoney cryftallifations, which may be confidered as 

 fublimed, and formed by the cryftallifation of fubftances re- 

 duced to the flate of fmoke or vapour. 



24. The nature of the flreams of cooled lava; their extent 

 and thicknefs. 



25. Whether it be true that, in general, they are porous 

 both at the upper and lower furfaces of the ftrata, and com- 

 padl in the interior part, 



26. To ftudy the nature of the different currents placed 

 above each other, in order to afcertain the difference that 

 may have taken place in the focus of the volcano, and even 

 in the fource of its lava. 



• To obftrvc thofc excavations from which confidcrable currents of air 

 iffue either periodically or conflamly. C. 



S 3 27, 79 



