POPOCATEPETL AND IxXTACCIHUATL—FARRINGTON. 97 
and sulphur. The latter is deposited about the vents. This sulphur, - 
where accessible, furnishes the source of supply to the miners. The 
escaping fumes cause considerable alteration of the surface of the 
lava walls and give them, especially on the southern side, a peculiar 
yellow color. The number and position of these vents seems to be 
variable. Packard quotes General Ochoa as stating that there are more 
than sixty. Felix and Lenk* state that Topf noted four in June, 
1886, while at the time of Dr. Lenk’s visit, December, 1887, there 
were seven. At the time of my visit there were six. Two of these, 
on the east and west crater walls, seem to have a pretty constant loca- 
tion, as do also two on the floor of the crater near the south wall. 
The floor of the crater is not level, but is heaped up with tumuli 
of various sizes from accumulations of material fallen from the crater 
walls. In the southeast portion is a little lake which varies in size 
at different seasons. Its supply comes from falling snow, which is 
nearly all melted by the warmth of the crater. The condensa- 
tion of the warm, moist air rising from the crater, upon meeting 
the cold of the summit, causes clouds, which may have been mis- 
taken by observers at a distance for smoke. The debris on the 
floor of the crater is constantly being augmented in quantity by rocks 
which fall from the crater walls. These are detached chiefly by the 
frost, which is continually at work. Sonntag} estimates the rise in 
the floor of the crater to be 0.65 of a foot a year from this cause, but 
calls attention to the obvious fact that the rise will be less every year, 
as the upper part of the crater expands. According to Aguilera and 
Ordofiez, the walls of the crater are growing constantly more nearly 
vertical, but this view has previously been criticised by the writer. { 
The view of distant places from the mountain was hindered 
by a sea of fleecy clouds which covered all below except only 
the peaks of Ixtaccihuatl to the north and Orizaba to the east. 
After about an hour spent upon the summit, descent to the ranch 
was made in less than one-fourth of the time required for ascent. 
The descent was attended with little difficulty, none of the hard- 
ships of the ascent being encountered. When there is sufficient 
snow on the slopes the Indian miners slide down on mats the 
entire distance, but this can be done only during the wet season. 
When part way down we passed through the clouds which enveloped 
the mountain. These appeared like a cold, drifting fog about a thou- 
sand feet in thickness. They were cumulus clouds, formed undoubt- 
edly by the cooling of the moisture of the air by the snow-covered 
*O%. cit. p. 25. 
tOP. cit. p. 58. 
tJour. Geol., Vol. IV, No. 4, p. 516. 
