122 Prof. T. G. Bonney. On the [June 19, 



ceons crnst. The difference, however, is probably of but little 

 importance. 



Besides the above specimens, Mr. Whymper placed in my hands 

 seven parcels of volcanic dust. The first (No. I) represents the 

 material strewn upon the roof of his tent, by the explosions which 

 occurred, as described above, during the night which he spent upon 

 the summit. The second (No. II) was obtained under circum- 

 stances hardly less remarkable. On July 3 Mr. Whymper made his 

 second ascent of Chimborazo. The morning was fine. Cotopazi, 

 some 65 miles away, was clearly seen, and at first " was not smoking 

 at all." At 5.40 A.M. an eruption suddenly commenced. "A column 

 of inky black smoke rose with immense rapidity 20,000 feet above the 

 top of the crater, that is to say, to a height of about 40,000 feet 

 above the sea ; was then caught by an easterly wind, borne at right 

 angles to its former course, then was taken by a northerly wind and 

 carried down upon us." But at 1.20 the dust had not yet reached 

 the summit of Chimborazo, and did not begin to fall till shortly after 

 the arrival of the party thereon; but during their brief stay (1 hour 

 10 minutes) it " fell to such an extent as to blacken the plateau all 

 over, so that it lost all resemblance to snow, and looked like a 

 ploughed field. This ash was wonderfully fine, and penetrated 

 everything, filled the working parts of instruments, rendered photo- 

 graphy a failure, and almost prevented us from eating, as our mouths 

 became filled with grit directly we opened them .... Extra- 

 ordinary and ghastly effects in the sky." The wind was strong from 

 the north-east, and bitterly cold. The ash continued to fall during 

 the whole of the descent, and during their absence had not only 

 covered but also filled the tent (pitched at a height of 15,950 feet). 



No. Ill is a specimen of the dust of the same eruption, which fell 

 at Ambato, between the two mountains, and about 45 miles from 

 Cotopaxi. 



No. IV (from the same) fell at Riobamba, due south of Cotopaxi 

 and at about the same distance as Chimborazo. 



No. V is a specimen of volcanic dust collected at Quito (35 miles 

 distant) during a great eruption which occurred in the year 1879, 

 when the material fell in such quantities that there was pitch dark- 

 ness for a time at midday. 



No. VI, another specimen of the same from Chillo, rather more 

 than 20 miles from Cotopaxi, where the flood caused by the eruption 

 did great damage. 



No. VII is a sample of an ash collected by Mr. Whymper from 

 hollows and sheltered places in the interior of the crater of Cotopaxi. 

 This he thinks the result of some more violent eruption than usual. 



The following is a description of the microscopic structure of these 

 volcanic dusts. 



