16 GEOLOGICAL MEMOIRS. 



waste, entirely without vegetation. All is black ashes ; and Mr. Har- 

 tung draws a vivid picture of the utter desolation of the tract. The 

 islanders, however, in order to increase their scanty means of 

 subsistence, have adopted the curious expedient of making funnel- 

 shaped holes through the ashes of the plain, and planting grain in 

 the old vegetable soil. On the summit of the Montana del Fuego 

 there is a vent which emits both smoke and very hot steam. The 

 ground has so high a temperature that a person cannot remain stand- 

 ing at the same place for more than a minute, and a stick thrust 

 through the ashes to the depth of a couple of feet is drawn up 

 charred at the end. 



The general strike of the volcanos of this period is nearly parallel 

 with that of the cones of the middle basalt-formation. Although the 

 great mass of the lavas, following the inclination of the ground, ran 

 to the west coast, one narrow stream found a passage to the east 

 coast by winding in a singular manner amongst the hills of the mid- 

 dle basalt-formation. In 1824 the inhabitants were again alarmed 

 by subterranean movements, and a volcano broke out a little to the 

 east of the Montana del Fuego. The products of this volcano (Vol- 

 can Nuevo) were however trifling ; a small stream of lava issued 

 from it, and ran towards the west coast, but did not reach the sea. 

 In the crater of this volcano is a bed of lava, which is pierced by 

 round holes, having an unknown depth. A stone thrown into 

 any of them is heard to strike the sides on some impediments for a 

 considerable time in its descent. One of these holes emits a small 

 quantity of steam. A calcareous deposit, of a yellowish-white colour, 

 encrusts all the preceding formations, except No. 4. This deposit is 

 similar in structure to that found in other localities {e.g. at King 

 George's Sound (Australia), in St. Helena, and at Porto Santo) ; its 

 origin has given rise to many different opinions. Mr. Hartung's 

 appears to be, that it has been formed by the decomposition of the 

 outer portion of the basalt throughout a long series of ages, for it is 

 not found on the summits of the peaks, but in the hollows, and on 

 the plains it has accumulated to a considerable depth, and it is absent 

 altogether from the newest lavas. It is composed of a carbonate of 

 lime, pure enough to be burnt into a material capable of use in build- 

 ing, and for this purpose it is quarried at Fuertaventura, and con- 

 veyed to Teneriffe. [J. Y. Johnson.] 



