GGQ 



DIKES OF LATA. 



[Ch. XXXI. 



was, to a certain degree, consolidated, it may have been rent open, so 

 that the lava ascended through fissures, the walls of which were per- 

 fectly even and parallel. After the melted matter that filled the rent 

 (fig. VI 6) had cooled down, it must have been fractured and shifted 

 horizontally by a lateral movement. 



In the second figure (fig. 7 17) the lava has more the appearance of 



Fig. 71G. 



Fig. 717. 



-0\ 



* 



c 







D *' 



Ground-plan of dikes near Palagonia. 

 a. Lava. 



&. Peperino, consisting of volcanic sand, mixed with fragments of 

 lava and limestone. 



a vein which forced its way through the peperino. It is highly 

 probable that similar appearances would be seen, if we could examine 

 the floor of the sea in that part of the Mediterranean where the waves 

 have recently washed away the new volcanic island ; for when a super- 

 incumbent mass of ejected fragments has been removed by denuda- 

 tion, we may expect to see sections of dikes traversing tuff, or, in 

 other words, sections of the channels of communication by which the 

 subterranean lavas reached the surface. 



Volcanic Hocks of Olot in Catalonia. — Geologists are far from being 

 able, as yet, to assign to each of the volcanic groups scattered over 

 Europe a precise chronological place in the tertiary series ; but I shall 

 describe here, as probably referable in part to the Post-pliocene and 

 in part to the Newer Pliocene period, a district of extinct volcanoes 

 near Olot in the north of Spain, which is little known, and which I 

 visited in the summer of 1830. 



The whole extent of •country occupied by volcanic products in 

 Catalonia is not more than fifteen geographical miles from north to 

 south, and about six from east to west. The vents of eruption range 

 entirely within a narrow band running north and south ; and the 

 branches, which are represented as extending eastward in the map, 

 are formed simply of two lava-streams — those of Castell Follit and 

 Cellent. 



Dr. Maclure, the American geologist, was the first who made 

 known the existence of these volcanoes ; * and, according to his de- 



* Maclure, Journ. de Phys., vol. lxvi. p. 219, 1808 ; cited by Daubeny, Descrip 

 tion of Volcanoes. 



