Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/882

798 violet clings to the soil, and above there is nothing but a little lichen. The number of wild flowering plants may be estimated at 900, upwards of 270 of which are peculiar to the Canaries. The forms of vegetation must in the main be considered North African, since the origin of many of those which they have in common with Southern Europe should be looked for in Africa. The character of the vegetation in Lanzarote and Fuerteventura islands, com posed of extensive plains and low hills, with few springs, is different from that of the other islands, which are more elevated and have many springs. The wood is more abundant, and the vegetation more luxuriant.

Geology.—Recent soundings have proved that the Canary Islands, like the other island groups of the North Atlantic, are the summits of mountains that are surrounded by an ocean of great depth. The lower and exterior portion of these islands consists for the most part of basalt, compact, vesicular, or scoriaceous, interstratified with beds of variously-coloured tufa. The compact variety of basalt frequently contains scattered grains and crystals of augite and olivine. In some cases the rock is chiefly trachyte. In Grand Canary the fossils contained in the tufas prove that movements of elevation began in the Upper Miocene period. They continued down to the Pleistocene period, for raised beaches containing shells of the recent period exist both in Teneriffe and Grand Canary. Simultaneously with the upheaval subaerial eruptions were taking place. Many of the superimposed streams of lava are divided from one another by red bands of laterite, probably ancient soils formed by the decomposition of the surfaces of the lava, and showing that the building up of the islands was a slow process. In Teneriffe the basalt and tufa form an exterior mass, through which in the centre emerge the felspathic or trachytic rocks forming the nucleus of the volcanic cone, and over them fragments of pumice and streams of modern lava have been thrown. These trachytic rocks contain numerous disseminated crystals of glassy felspar. Obsidian is found in several parts of Teneriffe, and is usually spotted with white crystals of felspar. The few minerals that have been found in the Canary Islands are those characteristic of volcanic regions. A little iron exists, but is not turned to account. In no part of Teneriffe has there been dis covered any sedimentary rock. The old lavas in Lanzarote are covered by a thin layer of white concretionary limestone, the origin of which is obscure, In Grand Canary and Fuerteventura there is also calcareous stone, but its nature does not appear to be known.

, the largest island of the group, lies between Grand Canary and Gomera. It is of irregular shape, 60 miles in length, with an extreme breadth of 30 miles, Not more than one-seventh is cultivable. A chain of mountains traverses the island in the direction of its greatest length, and in the middle of the broadest part rises the celebrated Peak, locally known as the Pico de Tcyde, which, with its supports and spurs, occupies nearly two-thirds of the whole island. It has a double top ; the highest point, El Piton, is 12,200 feet above the sea; the other, Chahorra, con nected with the first by a short narrow ridge, has a height of 9880 feet. They are both orifices in the same grand dome of trachyte. Neither reaches the line of perpetual snow. There is, however, a natural cavern, 11,050 feet above the sea, where snow is preserved all the year Snow remains about four months on the upper part of the Peak. For more than one-half of its circumference the base of the true peak rises from an elevated but comparatively level tract, called by the Spaniards El Llano de la Reto.ma (retama being the name of the Cytisus nubigenus which abounds there), and by the English the Pumice-Stone Plains. On the south-east, south, and south-west there is a high curved ridge overlooking the Pumice-Stone Plains, and presenting a very steep face to the Peak. This is the analogue of the Somma ridge of Vesuvius. Between the ridge and the sea the slope is more gradual, and there are intervening table-lands. A path used by the country people in going from one side of the island to the other crosses this ridge at the height of 8000 feet. Peaks rise from the ridge, one of which (Gtiajara) attains the height of 8900 feet. This ridge (the Llano) and the modern volcanic cone resemble in aspect a fortress with circular ramparts and a fosse. The ramparts are about 8 miles in diameter, and tower in some places more than 1500 feet above the fosse. They consist, as shown in the sections, of beds of trachyte, greenstone, and tufa of various thick nesses, and intersected by dykes and faults. On the north-west comparatively late eruptions have filled up the fosse. The modern cone, then, is a pile of lava, pumice, and ashes, thrown up in an ancient crater which had become greatly enlarged either by a falling in of the upper part of the cone, or by a series of violent explosions. Both El Piton and Chahorra have craters on their summits, from which issue steam and a little sulphureous vapour. The crater on El Piton is partly surrounded by a wall of lava, which has been made white by the action of sulphureous vapours, and every crevice contains small crystals of sulphur. The thermometer rises considerably when thrust into the ground. The crater is about 300 feet across, with a depth of; 70 feet. The average slope of the lower part of the cone is 28 ; that of the sugar loaf at the top is 33. The crater on Chahorra has a diameter of 4000 feet; its depth is scarcely 150 feet. The view from the highest point, when no clouds intervene, is very extensive. All the islands of the Archi pelago are visible, and the horizon is 140 miles distant. Neither the coast of Africa nor the island of Madeira is within the range of vision. The ascent of the Peak is usually made from Orotava, on the northern side of the island. After the cultivated grounds are left, the region of arborescent heaths is crossed. This zone extends over the zones of laurels and pines which have here disappeared. Above this is a belt covered with codeso (Adenocarpus frankenioides], and this extends to the region of retama, the first bushes of which are met with at the pass which admits the traveller into the Llano de la Retama. The scenery here is in striking contrast with what it has previously been. Instead of a steep and rugged ascent among black basaltic rocks, the traveller enters upon gently sloping ground, covered to a considerable depth with white pumice gravel, amongst which spring bushes of retama. The tender shoots of this shrub serve the wild goats for food, and the flowers yiold a rich honey to the bees. The entrance to the Llano at a sort of portal (called Portillo) between two basaltic hills, is about 7000 feet above the sea. Between two and three hours are consumed in crossing the Llano to the base of the cone, the lower part of which (Monton de Trigo) is ascended to a point 9750 feet above the sea, called E&tanda da, los Ingleses, where the mules are usually left, and where travellers frequently pass the night. Then conies the Malpays, 1000 feet in altitude, consisting of rough black lava streams broken up into blocks and stones. These cease at the neck called Eambleta, the lip of an older crater over which the lava poured before the sugar-loaf cone of pumice and ashes was thrown up. The pumice is in such quantity that at a distance it has the appearance of snow coating the Peak. From twenty to twenty-four hours are consumed in ascending the Peak and returning to Orotava, To the north-west of the grand cone some thousands of feet below Chahorra, there are many small cones of erup tion, showing that the intensity of volcanic action was greatest on this side. Eastward from the ridge bounding the Pumice-Stone Plains extends a chain of mountains to 