216 Professor Hoffmann on the Geological 
of the crust of our globe. Humboldt taught us for the first 
time that the focus of voleanic activity, which we find so 
abundantly and powerfully displayed in the region of the 
chain of the Cordilleras, must be regarded as standing in con- 
nection with another at a distance of hundreds of geographical 
miles; he shewed us how, in this respect, a kind of constant 
propagation of volcanic phenomena takes place ; at one time 
from south to north, and at another in a contrary direction. 
He pointed out the connection in which the littoral regions of 
the Mexican Gulf and the Antilles stand in relation to the 
series of earthquakes and volcanic eruptions; and how the 
operations of subterranean shocks are felt simultaneously over 
a space of several thousand square miles. 
We have to thank Humboldt for the investigation at the 
very place, and for the delineation of one of the greatest vol- 
canic catastrophes which has happened in historical periods — 
the eruption which, in September 1759, caused in a few days 
the production, on the plateau of Mexico, of the mountain of 
Jorullo, which has a height of 1578 German feet ; and which, 
moreover, caused to be formed out of it five other similar 
hills, and covered nearly four square German miles* to a height 
of 500 feet with lava, sand, and slag.t With this investiga- 
tion may be appropriately united, as one of the most remark- 
able results of this expedition, the discovery of the fact, that 
the continent of America, between the 18th and 19th de- 
gree (18° 59’ and 19° 12’), is intersected by a rent, 150 Ger- 
man miles long, extending right across from the coast of the 
Atlantic to that of the Pacific, and on which rise behind one 
another, and sometimes to upwards of 16,000 feet, the vol- 
eanos of Tuxtla, Orizaba, Puebla, Nevado di Toluca, Tanci- 
taro, and Colima. This rent is probably continued to a great 
distance in the South Sea; for, if prolonged westward, it would 
meet at a ‘distance of more than 50 German miles, the en- 
tirely volcanic Revillagigedo islands; and it is certainly not 
entirely accidental, that in its direction there should be found, 
in the midst of the South Sea, the Archipelago of the Sand- 
* The German mile = 43 English. 
+ Vue des Cordilleras, ii. 216. Essai Politique, vol. i. p. 248. 
