494 



CANARY ISLANDS. 



tch. xxix. 



Barlovenlo 

 Ft. 



ous, and almost always alternate with scoriae and perishable tuffs, so as to 

 be readily undermined, and most of them are speedily reduced to frag- 

 ments of a transportable size because they are divided by vertical joints 

 or split into columns. 



Canary Islands — Palma. — I have enlarged so fully in the " Principles 

 of Geology" on the different views entertained by eminent authorities 

 respecting the origin of volcanic cones, and the laws governing the flow 

 of lava, and its consolidation, that, in order not to repeat here what I have 

 elsewhere published, I shall confine myself in the remainder of this chap- 

 ter to the description of facts observed by me during a recent exploration 

 of Madeira and some of the Canary Islands. In these excursions, made 

 in the winter of 1853-4, I was accompanied by an active fellow-laborer, 

 Mr, Hartung, of Konigsberg. We visited among other places the beau- 

 tiful island of Palma, a spot rendered classical by the description given of 

 it in 1825 by the late Leopold Von Buch, who regarded it as a type of 

 what he called a " crater of elevation."* 



Palma is 46 geographical miles west of Teneriffe. Seen from the chan- 

 nel which divides the two islands, 

 Palma appears to consist of two 

 principal mountain masses, the de- 

 pression between them being at a 

 (map, fig. 642), or at the pass of 

 Tacanda, which is about 4600 feet 

 above the sea-level. The most nor- 

 thern of these masses makes, not- 

 withstanding certain irregularities 

 hereafter to be mentioned, a con- 

 siderable approach in general form 

 to a great truncated cone, having 

 in the centre a huge and deep 

 cavity called by the inhabitants 

 "La Caldera." This cavity (6, c, 

 d, e, fig. 642) is from 3 to 4 geo- 

 graphical miles in diameter, and 

 the range of precipices surrounding 

 it vary from about 1500 to 2000 

 feet in vertical height. From their base a steep slope, clothed by a 

 splendid forest of pines, descends for a thousand and sometimes two thou- 

 sand feet lower, the centre of the Caldera being about 2000 feet above 

 the sea. The northern half of the encircling ridge is more than 7000 

 English feet above the sea in its highest peaks, and is annually white 

 with snow during the winter months. 



Externally the flanks of this truncated cone incline outwards in every 

 direction, the slopes being steepest near the crest, and lessening as they 

 approach the lower country. A great number of ravines commence on 



Fuencaliente Pt. 



Map of Palma, from Survey of Capt Yidal, E. N. 



* ErhebuDg's Crater. 



