220 REACTION OF THE INTERIOR OP THE EARTH 



occupies the summit of the volcano, forms a deep circular 

 and often accessible caldron-like valley, the bottom of which 

 is subject to constant change. In many volcanoes the 

 greater or less depth of the crater is a sign of the greater or 

 less time elapsed since the last eruption. Long narrow 

 fissures from which vapours escape, or small circular hollows 

 filler) with substances in a state of fusion, alternately open 

 and close within the crater. The ground intumesces and 

 subsides, and mounds of scorise and cones of eruption rise 

 sometimes high above the surrounding wall of the crater, 

 giving the volcano a peculiar character, which may last for 

 years, until, during a new eruption, the mounds and cones 

 sink or otherwise disappear. The openings of such cones 

 of eruption, rising from the bottom of the crater, ought not to 

 be confounded, as they sometimes have been, with the crater 

 itself which incloses them. When the latter is inacces- 

 sible from its great depth and precipitous descent, as is the 

 case of Rucu-Pichincha, (14946 French feet in height), the 

 traveller may look down from the edge on the summits 

 which rise from the depth below, through the sulphureous 

 vapours by which the valley of the crater is partially filled. 

 This spectacle is a magnificent one. I have never seen 

 nature under an aspect more grand and wonderful than in 

 the view from the edge of the crater of Pichincha.. In the 

 interval between two eruptions, a crater may either offer to 

 the eye no phsenomenon whatever of incandescence, but 

 merely open fissures from which steam issues ; or the geo- 

 logist who is able to approach the cones of scorise without 

 danger over a soil only slightly heated, may enjoy the view 

 of the eruption of burning fragments which fall back on the 

 flanks of the mounds from whence they have issued. Each 



