638 AQUEOUS EROSION IN PALMA. [Ch. XXIX. 



gravel formed, to be afterwards cut through to a depth of 800 feet ? 

 The ravine through which the torrent now flows has been excavated 

 to that depth through the old conglomerate. The occurrence of two 

 or three layers of contemporaneous lava, intercalated between the strata 

 of puddingstone, ought not to surprise us ; for even in historical times 

 eruptions have been witnessed in the southern half of Palma. Such 

 basaltic lavas, one of them columnar in structure, had not come down 

 from the Caldera, but from cones much nearer the sea, and immediately- 

 adjoining the Barranco, like the cone of Argual (see map, p. 629) and 

 others. These lavas, of the same age as the conglomerate, consist of 

 three or four currents of limited extent, for in many parts of the river- 

 cliffs no volcanic formation is visible on either bank. On the right 

 bank of the Barranco, the conglomerate, when traced westward, is soon 

 found to come to an end as it abuts against the lofty precipice e (fig. 



Fig. TOO. 

 West. 



East. 



/J^/i'J Ji"'"' "— 2^ia- 



A. Eavine or Barranco de las Angustias, near its termination in Palma. 

 &, &', V. Conglomerate 800 feet thick in parts. 



c, c'. Lava intercalated between the beds of conglomerate. 



d, d f . Another and older current of basaltic lava, columnar in parts. 



E. Cliff of ancient volcanic rocks of the Upper Formation (p. 634), a prolongation of 



the western wall of the Caldera. 



F. Platform on which the town of Argual stands. 



700), which is a prolongation of the western wall of the Caldera. Its 

 extent eastward from b, may be more considerable, but cannot be 

 ascertained, as it is concealed under modern scoriae and lava spread 

 over the great platform, f. 



As we could find no organic remains in the old gravel, we have no 

 positive means of deciding whether it be fluviatile or marine. The 

 height of its base above the sea, where it is 800 feet thick, may be 

 about 350 feet, but patches of it ascend to elevations of 1000 and 

 1500 feet near the top of the Barranco, as shown at k, &c, in section, 

 fig. 699 p. 631. Such a mass of gravel, therefore, bears testimony 

 to the removal of a prodigious amount of materials from the Caldera 

 by the action of water. Whatever may have been the mode of 

 transportation, it is obvious that a large portion of the volcanic mate- 

 rials, consisting of sand, lapilli, and scorise, before described (p. 632) 

 as belonging to the upper formation in the Caldera, would leave 

 behind them few pebbles. Nearly all of these perishable deposits 



