THE PLANTS AND GARDENS OF THE CANARY ISLANDS. 63 
From the geological point of view the Canaries are singularly 
interesting. They are almost entirely of volcanic formation, 
and are really the peaks of submerged mountains— a con- 
tinuation of the Atlas chain running westward into the 
Atlantic. The last eruptions took place in 1796 and 1798. 
Cones of ash and scoriae — veritable cinder-heaps — mounds of 
volcanic mud of various colours, and rugged masses of lava 
extending for miles across the country bear abundant evidence 
of the origin of the islands. To get at the volcanic dust for 
soil it is often necessary, for instance in Teneriffe, to blast the 
solid lava and pile it up in heaps. This gives some parts of 
the country the appearance of an extensive stone quarry. In 
Grand Canary, where volcanic mud is more widely distributed, 
the cultivated areas are more easily reclaimed. The soil, where 
existing, is very rich and fruitful. The area suitable for cultiva- 
tion is, however, comparatively small. Only about one-seventh 
of Teneriffe is capable of bearing crops, and the proportion in 
the other islands is equally limited. The land is usually very 
steep and stony. In fact, along the coast the aspect is singularly 
barren and desolate. It is only in the interior valleys, under 
the influence of irrigation, that crops can be successfully 
cultivated. Green slopes with grass {monte verde) are met with 
in the cloud region at an elevation of 2,500 to 4,000 feet. This 
is the region of the evergreen trees and shrubs. In Teneriffe 
above this there is a sub-alpine region with a dry climate, where 
only a few plants flourish. Humboldt visited Teneriffe at the 
end of the last century. His review of the vegetation is given 
in his " Personal Narrative " (chap, ii., Bohn's ed., 1852). The 
first zone he termed that of the Vine, extending from the sea- 
shore to about 1,000 feet elevation. It is that which was most 
inhabited, and the only part carefully cultivated. The native 
plants found were tree-like Euphorbias, Dragon trees. House- 
leeks, and shrubby Sow-thistles. The cultivated plants were 
Date-palms, Bananas, Sugar-cane, European fruit-trees, the Vine, 
and Corn. The second zone, in addition to the grassy slopes, 
comprised the Laurels of several species, a native Olive, Hollies 
an Arbutus, the Canary Ivy, numerous Ferns, Buttercups, and 
the native Foxgloves. The cultivated plants were chiefly Sweet 
Chestnuts and fodder plants. 
The third zone with the Candleberry Myrtle {Myrica), the 
