[Footnote 71: See an account of a journey to the top of the Pic of Teneriffe, in Sprat's History of the Royal Society, p.200, &c. Glas also went to the top of it.--History of the Canary Islands, p. 252 to 259. In the Philosophical Transactions, vol. xlvii. p. 353-356, we have observations made, in going up the Pic of Teneriffe, by Dr T. Heberden. The doctor makes its height, above the level of the sea, to be 2566 fathoms, or 15,396 English feet; and says, that this was confirmed by two subsequent observations by himself, and another made by Mr Crosse, the consul. And yet I find that the Chevalier de Borda, who measured the height of this mountain in August 1776, makes it to be only 1931 French toises, or 12,340 English feet. See Dr Forster's Observations during a Voyage round the World, p. 32.--D.] "To the eastward of Santa Cruz, the island appears perfectly barren. Ridges of hills run toward the sea; between which ridges are deep valleys, terminating at mountains or hills that ran across, and are higher than the former. Those that run toward the sea, are marked by impressions on their sides, which make them appear as a succession of conic hills, with their tops very rugged. The higher ones that run across, are more uniform in their appearance." "In the forenoon of the 1st of August, after we had anchored in the road, I went on shore to one of these valleys, with an intention to reach the top of the remoter hills, which seemed covered with wood; but time would not allow me to get farther than their foot. After walking about three miles, I found no alteration in the appearance of the lower hills, which produce great quantities of the _euphorbia Canariensis_. It is surprising that this large succulent plant should thrive on so burnt-up a soil. When broken which is easily done, the quantity of juice is very great; and it might be supposed that, when dried, it would shrivel to nothing; yet it is a pretty tough, though soft and light wood. The people here believe its juice to be so caustic as to erode the skin;[72] but I convinced them, though with much difficulty, to the contrary, by thrusting my finger into the plant full of it, without afterward wiping it off. They break down the bushes of _euphorbia_, and, suffering them to dry, carry them home for fuel. I met with nothing else growing there, but two or three small shrubs, and a few fig-trees near the bottom of the valley." [Footnote 72: Glas, p. 231, speaking of this plant, says, "that he cannot imagine why the natives of the Canaries do not extract the juice, and use it instead of pitch, for the bottoms of their boats." We now learn from Mr Anderson their reason for not using it,--D].