Ascent to the Summit of the Popocatepetl. 229 
which forms the bottom; now I twice saw blocks of a tolerable size 
detach themselves: I watched them as long as it was possible, and 
the noise we heard corresponded precisely with the shocks they met 
with in fallmg. I therefore think that the kind of lengthened deto- 
nations which occasionally occurred, proceeded from similar causes. 
M. de Gerolt spoke of subterranean’ action, and of the expansive 
force of vapor. We were perhaps both right, for if, owing to caus- 
es easy to conceive, the stones were to obstruct the vent-holes, the 
vapor would not be long ere it would disengage itself with violence 
and noise from the obstacles opposed to its passage. 
You have doubtless read in the histories of the Conquest, that 
Don Diego Ordaz, one of Cortes’ officers, went up to the volcano 
for sulphur to make powder. ‘There were perhaps at that time 
some fissures on the side of the mountain where it deposited itself, as 
is now to be seen in Italy. I do not think it is possible to get at 
that which is in the crater; and it is probable that in Fernand Cor- 
tes’ time the volcano was more active than at present. There are 
millions of quintals of sulphur at the bottom of the funnel; the air 
is infected by the emanations. I have no doubt, that a person let 
down would be suffocated by the sulphurous vapor before having 
reached a-depth of two hundred feet. Now, two hundred feet are 
not a fourth of the distance to the yellow masses which cover the 
bottom. Even supposing that one could breathe therein, the ropes 
required to go only to the nearest inclined plane would have to be 
of a prodigious length ; and how are they to be got up to the top of 
the volcano, when it is so difficult to get there oneself, and that the 
least weight is almost an intolerable burthen ? I am therefore of opin- 
ion, that if Diego Ordaz gathered sulphur on the Popocatepetl, it could 
only have been at a little above the volcanic sands, and not in the 
crater. 
- By half-past three we had terminated our experiments, made 
sketches, and fixed our flag on the highest pomt of the voleano. At 
four o’clock we were in the hollow way opposite the Pico del Fraile, 
where our guides were waiting for us. We made them a sign to 
return to the tent, and we continued to descend by a different route 
from that which we had ascended. At five we were on the borders 
of the wood. We observed several blocks of porphyry which had 
fallen recently from the summit; probably at the time of the earth- 
quakes on the 13th and 15th of March. ‘They had made a deep 
furrow from the top of the sands to midway down the mountain ; but 
