360 ASCENSION. [CHAP. xxi. 



A hill, formed of the older series of volcanic rocks, and which has 

 been incorrectly considered as the crater of a volcano, is remarkable 

 from its broad, slightly hollowed, and circular summit having been 

 filled up with many successive layers of ashes and fine scoriae. These 

 saucer-shaped layers crop out on the margin, forming perfect rings of 

 many different colours, giving to the summit a most fantastic appear- 

 ance ; one of these rings is white and broad, and resembles a course 

 round which horses have been exercised ; hence the hill has been 

 called the Devil's Riding School. I brought away specimens of one 

 of the tufaceous layers of a pinkish colour ; and it is a most extra- 

 ordinary fact, that Professor Ehrenberg * finds it almost wholly com- 

 posed of matter which has been organized : he detects in it some 



siliceous-shielded, fresh-water infusoria, and no less than twenty-five 

 different kinds of the siliceous tissue of plants, chiefly of grasses. 

 From the absence of all carbonaceous matter, Professor Ehrenberg 

 believes that these organic bodies have passed through the volcanic fire, 

 and have been erupted in the state in which we now see them. The 

 appearance of the layers induced me to believe that they had been 

 deposited under water, though from the extreme dryness of the climate 

 I was forced to imagine, that torrents of rain had probably fallen during 

 some great eruption, and that thus a temporary lake had been formed, 

 into which the ashes fell. But it may now be suspected that the lake 

 was not a temporary one. Anyhow, we may feel sure, that at some 

 former epoch, the climate and productions of Ascension were very dif- 

 ferent from what they now are. Where on the face of the earth can we 

 * Monats. der KOnig. Akad. d. Wiss. zu Berlin. Vom April, 1845. 



