344 Volcanoes. 



the soundest thoughts may pass for error and " most extra- 

 ordinary hallucination," in the view of those whose information 

 or judgment happens not to be of a first-rate description. 

 It may suit the quibbling turn of mind occasionally imputed 

 to the profession to which the signature of Causidicus implies 

 him to belong, to allege, as he does, that " Dr. Murray en- 

 tirely changes the terms of his proposition. There is a vast 

 difference between 'a decided connection' and 'an unvarying 

 and necessary relation.' " I shall only add that Causidicus is 

 welcome to view me as standing upon either of the positions 

 which he appears to have in his eye ; and I am persuaded 

 the footing is firm enough to enable me to defy such efforts 

 as his. I am, Sir, yours, &c. 



Aberdeen, April 17. 1833. Alexander Murray. 



The above communication relates strictly to the connection 

 between rocks and plants. On the relation between soils and 

 plants, see Mr. Goldie, in Gard. Mag., vol. ii. p. 125.; Mr. 

 Gordon, in vol. iv. p. 463. ; Causidicus, in vol. vi. p. 216.; 

 Mr. Gordon, in vol. vi. p. 359. ; Causidicus, in vol. vii. p. 371., 

 vol. ix. p. 291. — J.J). 



Art. VIII. Volcanoes. By W. M. Higgins, Esq. F.G.S., Lec- 

 turer on Natural Philosophy in Guy's Hospital, and J. W. 

 Draper, Esq. 



{Continued from Vol. V. p. 637.) 



GEOGRAPHICAL POSITION AND HISTORY OF ACTIVE 

 VOLCANOES. 



Africa. — The continent of Africa does not offer a single 

 example of an active volcano; but nearly all the neighbouring 

 islands are of volcanic origin, and many of them present ex- 

 amples of active vents. 



The whole group of the Canaries is the product of some 

 vast subaqueous volcano, to the furnaces of which the various 

 islands seem but as openings. 



Teneriffe is the first of these to which our attention is 

 drawn. The Peak of Teneriffe is one of the most elevated 

 volcanic mountains, and lifts its towering head to a height of 

 12,176 feet above the level of the sea. It is a pyramidal 

 mass, having a base of more than 115,110 yards in circum- 

 ference. The cone is small in proportion to the mountain, 

 and is said to be not more than 537 ft. high. Its crater is 

 about 300 ft. in its greater diameter, 200 ft. in its lesser, 

 and 100 ft. deep. It is not, however, from this that the 



