82 CANARY ISLANDS. 



fracrments of pumice-stones, which are often reduced to 

 powder resembling a.'^lies. In examining them with a lens, 

 there may be discovered among them, minute particles of 

 feldspar and pyroxene. This llano separates the dark, 

 basaltic, and earth-like lavas from the vitreous and feld- 

 spathic varieties, the bases of the latter being obsidian, 

 pitch-stone, and pyroxene. Tiie feldspathic lavas are 

 destitute of hornblende and mica, and are of a blackish- 

 brown, often varying to the deepest olive-green. They 

 contain large crystals of feldspar which are not fissured, 

 and seldom vitreous. Yv^hen the basis of the feldspathic 

 lava changes from pitch-stone to obsidian, the color is paler 

 and mixed with gray ; in this case, the feldspar passes by 

 imperceptible gradations from the common to the vitreous. 

 Sometimes both varieties are found in the same fragment. 

 There are three varieties of obsidian met with, on the 

 Peak. The first occurs in large blocks several yards long, 

 which often have a globular figure. It contains a quantity 

 of vitreous feldspar, of a snowy whiteness, and has a most 

 brilliant pearly lustre. It is of a brownish-black, but little 

 translucent at the edges, and has an imperfect conchoidal 

 fracture, and passes into pitch-stone. The second variety 

 is found in much smaller fragments, and is generally of a 

 greenish-black, but sometimes of an obscure gray, and 

 very seldom of a jet black. Its fracture is perfectly con- 

 choidal, and is extremely translucent at the edges. The 

 third variety is the most remarkable of the whole, from its 

 connexion with pumice-stones. It is like the former, of a 

 greenish-black, and sometimes of an obscure gray, but 

 occurs in very thin plates, alternating with layers of pumice- 

 stone. The fibres of the pumice-stone are very seldom 

 parallel to each other, and perpendicular to the strata of 

 obsidian ; they are most commonly irregular, and abestoi- 

 dal, and instead of being disseminated in the obsidian, 

 they are found simply adhering to one of the external sur- 

 faces of the substance.* 



*Obsi'lian was c.ille.l by the Guanches, tabona, the splinters of which they 

 fixed to their lances, instead of iron. Tliey carried on a considerable trade in it 

 with such of the neighboring islands, as were accessible to them. 



