1884.] Microscopic Structure of some Rocks from Ecuador. 117 



third of the crater, and gradually inspected the whole of it as the 

 wind shifted the smoke hither and thither. 



" On the first occasion that we mounted to the edge of the rim, we 

 had been standing there only a few minutes, when a loud roar 

 occurred at the bottom of the crater, and volumes of steam were 

 ejected, which rose to our level in two or three seconds, spread out in 

 vast clouds, and were gradually dissipated. We looked at each other 

 with alarm, not knowing what was going to happen. We probably 

 all thought alike that an eruption was about to occur, and that we 

 had best run for our lives. As quiet reigned again, we remained, and 

 found that such explosions occurred about every half-hour during our 

 stay on the summit. The vapour ejected appeared to be pure steam, 

 and it appeared to issue from the (roughly) circular orifice at the 

 bottom of the crater. It rose with great rapidity, taking, I think, 

 not more than two to three seconds to rise the 1,200 feet from the 

 bottom of the crater to the level of the rim. When it reached us it 

 could not be said even to be warm, and it was quite devoid of 

 odour. The explosions were momentary the affair of an instant 

 and during the instants of their occurrence the noise resembled 

 that which is made when large ocean steamers are blowing off steam. 



" In course of time, as eddies of wind shifted the vapour in the crater 

 from one to another part, we gradually made out its general form and 

 nature. Its form above is roughly oval, and at the bottom rudely 

 circular. The general angle from the edge of the rim to the bottom 

 exceeds 45. The mean of a great number of observations would 

 perhaps be about 48. At no part is there a continuous slope from 

 top to bottom. The amphitheatre is made up of a large number of 

 oliffs (often vertical, and even overhanging), and of slopes of all 

 degrees. This character continues all the way down. The upper part 

 was. not noticeably fissured, but from about half-way down, down to 

 the bottom, cracks and fissures were numerous ; and from these aper- 

 tures vapours of various tints were lazily issuing some white, greyish, 

 or dark, but none were inky black. These vapours perpetually 

 obscured the inferior part of the crater, the influence of the wind not 

 being felt so low down. From this cause, I am unable to state posi- 

 tively from what part the ejections of steam occurred which have 

 been referred to above. 



" In the evening of February 18th, when it became dark, I went 

 again to the edge of the crater to view the interior. Less smoke 

 appeared to be issuing from the cracks at the bottom, and it did not 

 now prevent the examination of any part. The fissures for several 

 hundreds of feet from the extreme bottom of the crater were now 

 radiant with heat, and the lowest part was occupied by a circular, 

 glowing, fiery spot, which I estimated to be 180 feet across, or 

 about one-tenth of the entire diameter of the crater. I examined 



