241 



ed, that these stones were extracted from a 

 quarry near Rambla ; and that there were simi- 

 lar quarries near Realejo, and the mountain of 

 Roxas, above Adexa. This information, pro- 

 bably not very accurate, led me into an error. 

 As the coasts of Portugal consist of basalts co- 

 vering calcareous rocks containing shells, I 

 thought, that a trappean formation, like that of 

 the Vicentin in Lombardy, and of Harutsch in 

 Africa, might have extended from the banks of 

 the Tagus and Cape St. Vincent as far as the 

 Canary Islands ; and that the basalts of the 

 Peak might perhaps conceal a secondary calca- 

 reous stone. I mentioned these ideas in a letter, 

 which was not intended to be made public ; and 

 they have exposed me to the severe reprehension 

 of a naturalist, according to whom every volca- 

 nic island is only an accumulation of lavas and 

 scoriae, and who admits no fact contrary to his 

 own theory of volcanoes*. 



Though TenerifFe belongs to a group of islands 



* Examination of certain geological opinions of Mr. de 

 Humboldt, by Mr. G. A. De Luc (Journ. de Phys. t. 50, P. 

 1, p. 114). This memoir, in which we recognise an excellent 

 observer, is the continuation of another against Mr. Kirwan, 

 who thinks, that the lavas of Vesuvius repose on the cal- 

 careous beds of the Apennines. Ibid. vol. xlix. p. 23. 

 According to the Theories of Volcanoes, given by Mr. De Luc, 

 it is impossible, that a real lava should contain fragments 

 of vegetable substances. Our collections, however, contain 

 pieces of trunks of palm-trees, enclosed and penetrated by the 

 VOL. I. R 



