HARTUNG — CANARY ISLES. 15 



heavals. The direction of the valleys is outwards from the hills, 

 being parallel where the line of heights is straight, and radiating 

 when curved. The sides of the valleys are by no means vertical, but 

 inclined at an angle of about 30° ; the floors are flat, and the valleys 

 themselves have been so much widened by lateral breaches that the 

 interjacent ridges have been reduced at their summits to a line of peaks 

 more or less detached. 



The basalts of this formation resemble in general structure those of 

 Madeira. They are, however, a good deal more varied than the 

 latter in their lithological character and contents. For instance, in 

 some places are found very large pieces of augite imbedded in a 

 basaltic paste ; at others, various crystallized minerals or small amor- 

 phous materials are met with in a matrix of basalt. 



3. The middle Basalt-formation.— hi the first glance the oldest 

 parts of this formation appear to be of the same age as the preceding, 

 but they may be distinguished by the fact that the forms of the 

 cones, craters, and lava-streams may be clearly made out. The lavas 

 are already covered with a thin layer of vegetable soil, which sup- 

 ports scanty crops of grain, whilst the most modern lavas only sup- 

 port a plant here and there. This formation is altogether wanting 

 in the south-western part of Fuertaventura. The first cone on that 

 side is met with in the middle of the syenite and trap formation. 

 Two others are in its north-eastern border. In the remaining parts 

 of the island there are about twenty cones, mostly detached ; but 

 altogether the space occupied by this formation forms a comparatively 

 small portion of the surface in Fuertaventura. In the other island, 

 however, it occupies nearly one-half of the whole. About the mid- 

 dle of the island is a chain of cones extending in the direction of the 

 longer axis, the highest of which has an altitude of 1959 feet. In 

 other parts are many detached cones ; one, called Corona, with a 

 very perfect crater, at the north-east extremity of the island, reaches 

 the height of 1940 feet. The four islets, Graciosa, Clara, Allegranza, 

 and Lobos, belong to this formation. In the lava which flowed from 

 Corona, Mr. Hartung remarked one of those subterranean channels not 

 uncommon in volcanic districts ; but, singular to relate, he found that 

 its floor was the roof of a similar channel underneath. A stream of 

 lava flowing in the opposite direction fell over the cliffs of the north 

 coast, and is a conspicuous object to this day. Of these two phe- 

 nomena Mr. Hartung has given sketches. 



4. The newest Basalt-formation. — In the year 1730 violent sub- 

 terranean commotions commenced in Lanzarote, which continued for 

 six years. During this period a fourth part of the island was laid 

 waste by the materials ejected. Villages were overwhelmed, cattle were 

 destroyed, and the inhabitants fled from the island . A large district 

 on the west coast, the floor of which is about 900 feet above the sea, 

 was formed by this series of eruptions. The chief elevations are a 

 line of cones with craters, out of which the lavas, ashes, &c. issued, 

 which covered the surrounding country. The highest point, and in 

 every way the most striking mountain, is the Montana del Fuego, 

 with an altitude of 1 750 feet. The surrounding district is an utter 



