Some Account of the Island of Tener'iffe. 25 1 



wards tlie bottom. This basaltic lava contains olivine and horn- 

 blende, and, in the caves on the coast, zeolite. This substance 

 is also found in stalactites and iu masses, sometimes in layers 

 spread between the strata and diffused over the rock. 



Nodules of chalcedony are sometimes also found ; but these 

 substances occur only in the chain of mountains towards the 

 north-east, from the northern extremity of Santa Cruz to the 

 point of Hidalgo. 



The lavas of the island are of an endless variety, and the num- 

 ber of streams that have flowed are much beyond all enumera- 

 tion. The whole surface is either ash, or solid or decompoood 

 lava, which seems again and again to have been perforated l)y 

 volcanic eruptions ; the number of small extinct volcanoes is 

 prodigious, they are to be found in all parts of the island, but 

 the stream that has flowed from even the largest of them, such 

 as the lava of the Peak called El Mai Pais, is trifling in com- 

 parison with that immense mass of lava mountains wliich con- 

 stitute the central chain of the island, and which stretch out as 

 headlands like those of Las Horcas and San Ursula. 



I never found in situ those masses of columnar basaltic rock 

 that are so common in the island of .Madeira: but in the valley 

 of Las Espernnzn'>, in the chain of hills to the north-eastward 

 of the town of Santa Cruz, they lie scattered about in consider- 

 able numbers, and M. Escolar told me that he liad seen strata 

 of them to a considerable extent, exhibiting with precision the 

 columnar bas.iltic form : the modern lavas of the peak are all 

 basaltic, that of 1704 is decidedly so, as well us that of 179S, 

 though not exhibiling any prismatic form. Prisms of basaltic 

 lava are yet found on the peak : I picked up one, though there 

 are no strata of them to be met with. The metals are rare, and 

 afford but little variety: specular and micaceous iron, black and 

 grey manganese are all that have hitherto been discovered. 

 The salts that are so conunon on Vesuvius, are here seldom met 

 with, Augite is also rare, and mica and leucite, though care- 

 fully sought after, have hitherto not been found. 



In that part of the island between Laguna and Tacaronte, 

 where there are few streams of lava, the soil is evidently volcanic. 

 I examined many of the clods that were turned up by the plough, 

 and found them all alike : they contained much strong clav, with 

 crystals of feldspar, olivine, and specular iron. Dr. Gillan, who 

 acco?npanied Mr. Barrow and Sir G. Staunton, has advanced an 

 opinion, that between Laguna and Malanzos there are no signs 

 of volcanic formation. That the currents of lava occur but sel- 

 dom is most true ; but the mountains in the vicinity of Laguna 

 are all volcanic, and one has a visible crater: besides, the assertion 

 would prove too much ; for it would go to maintain that the 



Campagna 



