B. Hobson—WMezxican Volcanoes. 9 
It is of regular conical form, its summit broadly truncated by 
a comparatively large crater. Its sides slope at angles varying from 
28° to 35°, the higher angle being met with on its southern and 
western sides. It appears most symmetrical as seen from the south, 
on which side, more especially, its slopes are traversed by numerous 
narrow, deep, and straight radiating furrows or barrancas due to 
erosion. It is most impressive as seen from the west, as on that side 
its height above its base is greatest. Seen from the west the latest 
(No. iv) lava-flow rises as a lofty black prominent and very con- 
spicuous ridge forming an unsymmetrical appendage on the north side 
of the cone. (See Plate I, Fig. 1.) 
To resume the account of our visit. August 28th. In the early 
morning we walked down the hill at Mata de Platano, crossed the 
stream at its foot, and followed a dry stream bed, in well-stratified 
black lapilli of Jorullo, to the east side of the cone, where the ascent 
proper began. ‘The outer slope of the cone is composed of completely 
incoherent black lapilli mostly about the size of peas. In this soil 
grows from foot to summit of the cone a dense tropical vegetation of 
mimosas or acacias and other trees (reaching 15 or 20 feet in height), 
shrubs, grass, and maidenhair ferns. The grass does not form a con- 
tinuous covering, but everywhere the lapilli are exposed, and nothing 
essential appears to be concealed, so that the luxuriant flora can hardly 
be considered a drawback by the geologist, while it greatly adds to the 
attractiveness of the ascent. We were half-way up the cone when 
a tropical downpour of rain began and lasted half an hour. The sky 
cleared and we soon reached the north-eastern summit of the crater 
rim which Mr. E. Ordditiez has christened Pico de Humboldt. From 
this point there is a splendid view of both the immediate neighbourhood 
and the more distant country. 
The Crater. 
The first feature to arrest our attention was the crater. It is ovoid 
in form, and measures along its major axis from north to south 
568 yards by 421 yards from. east to west, and its depth from the 
highest part of the rim is 489 feet. A breach 500 feet wide and 
about 200 feet deep has been formed on the northern side by the last 
outflow of lava. While the exterior of the cone consists of lapilli and 
agelomerate the interior of the crater forms an inverted conical cavity 
coated with lava weathered to a reddish brown and almost bare of 
vegetation. A series of curved fissures formed by the contraction 
of the lava in cooling has allowed the inner lava lining of the crater to 
sink in a series of ferraces bounded by steep or vertical walls. The 
rim of the crater is a mass of very scoriaceous rough lava, very difficult 
to walk over, and in places very narrow. We “aul our way, however, 
along it to the west side of the rim, whence a bird’s-eye view of the 
lava. streams is obtained. 
The Lava- Streams and Fumaroles. 
Ordénez! gives an excellent geological map, scale z5d00 or 
211 inches to 1 mile, of the “Jorullo volcanoes (from which, 
> Loe. cit. 
