1817.] GEOLOGY OF THE WEST INDIES. 141 



in a state approaching to ignvtion, resembling a current of 

 lava; burning the woods, and filling all the channels of 

 the little rivers that descend the mountain, rising some- 

 times to the height of three or four hundred feet. 



This irruption consisted of a great quantity of angular 

 sand; the broken masses of roasted and vitrified rocks 

 being mixed with loose angular pieces of all sizes, brittle, 

 and crumbling under the hammer. These in.bedded 

 rocks are, 1st. A rock resembling a small and* middling 

 sized grained granite, roasted, with diaphanous feldspar. 

 2d. A gray rock, in plates, like gneiss, but much altered 

 by the fire. 3d. A feldspar and hornbiend rock, the feld- 

 spar crystallized and diaphanous, with the appearance of 

 having been roasted. 4th. A hornbiend rock, crystalline, 

 having a roasted appearance. 5th. A dark coloured rock, 

 with a conchoidal, even, vitreous fracture, containing 

 crystals of feldspar, some pieces so vitreous as to resem- 

 ble pitch stone, and porphyry running dirough all the gra- 

 dations from a gray rock, scarcely vitrified, to a total vit- 

 rification, and thence to a porous scoria, not unlike pumice, 

 with transparent crystals of feldspar, taking a deeper tinge 

 of black in proportion to the degree of vitrification. 6th. 

 A bluish rock widi feldspar, and some black crystals, 

 having all the appearance of compact lava. If one sup- 

 poses that volcanic action tends to form large cavities un- 

 der the places whence the lava, &c. issues, and that one, 

 or more, of these cavities, where the combustible materials 

 are exhausted, becomes fiUed with water, while other cavi- 

 ties, where these materials still remain, are filled with lava, 

 Sec. it would appear only necessary to unite the contents 

 of two such caverns to produce all the effects of an irrup- 

 tion of cinders. 



