B. Hobson—WMevxican Volcanoes. Le 
south-west of the main cone, rises to 3,592 feet or 394 feet above its 
base. In all three cases the western base is 180 feet lower than the 
eastern. Between the main cone and the Voleancito de Enmedio are 
several mounds of volcanic sand and lapilli, which have been regarded 
by previous observers as additional cones, but which, according to 
Ordonez, show horizontal bedding-planes and not the structure 
characteristic of cones of eruption. he outer slopes of the volcancitos. 
are as steep as those of the main cone, reaching as much as 35°. All 
three volcancitos are horse-shoe shaped, being breached on their 
western side. Mr. Orddnez gives an explanation of this breaching 
which I find it difficult to accept. He says:? “En effet, ces cones, 
peu Glevés et Vun volume relativement faible, reposaient sur la lave, 
alors incomplétement solidifiée ; et celle-ci dans son mouvement lent: 
de descente, entraina avec elle, la partie de ces édifices, qui avait pour 
base cet instable piedestal, et leurs pans détachés, perdirent l’équilibre 
et se réduisirent en morceaux.” I should have thought it more 
probable that each was breached in the ordinary way by an outflowing 
lava-stream, but Mr. Ordonez maintained that such was not the case, 
and time did not permit me to settle the question by an poeanans 
examination of the ground. 
The voleancitos are characterised by the abundance of ‘volcanic 
bombs, which occur in their cones and appear to be absent from, or 
scarce 1n, Jorullo proper. ‘hese bombs are spherical, ellipsoidal, or 
fusiform, and sometimes show the fractured concentric layers known 
as bread-crust structure. They are mostly as big as a man’s head, 
but may reach a cubic metre in size. On our way back from Jorullo 
to Mata de Platano on August 28th, we saw many excellent examples. 
of them in the southern slopes of the Volcancito del Sur. On 
August 29th we left Mata de Platano and walked along the eastern 
foot of Jorullo, and then turned westwards along the southern side of 
the Volcancito del Norte and the northern edge of the latest lava- 
stream of Jorullo, afterwards crossing flows Nos. i, u, and 1, 
which are more or less covered with vegetation which is not dense, 
the trees occurring scattered as in a park. 
The Hornitos. 
We examined several ‘hornitos’ (literally ‘little ovens’). These 
are circular or elliptical mounds, generally perhaps 10 to 15 feet long 
and 3 to 5 feet high, consisting externally of numerous layers of 
incoherent small black lapilli or volcanic sand, each layer from one-fifth 
of an inch to 2 inches in thickness, arranged concentrically and 
parallel to the outer surface, forming domes with qua-qua-versal dip 
of the layers. Most of the hornitos have an opening through which 
gases and vapour formerly escaped, and they all contain a solid or 
hollow nucleus of the underlying basaltic lava.* They are simply 
surface vapour vents of the lava- streams coated with layers of voleanic 
sand and lapilli which, occurring in thick accumulations near the four 
cones, overspread the older lava-streams of Jorullo, but not the latest, 
which hence appears to be the result of the final effort of the volcano. 
1 Loc. cit.. p. 36. 
2 For details see the paper by Ordéiiez already mentioned. 
