196 REACTION OF THE INTERIOR OF THE EARTH 



distance of 436 miles, and by the colossal mountain masses 

 of Quito, Pasto, and Popayan, as well as by countless val- 

 leys and ravines. The sound was clearly not propagated 

 through the air, but through the earth, and at a great depth. 

 During the violent earthquake in new Granada in February 

 1835, subterranean thunder was heard at Popayan, Bogota, 

 Santa Martha and Caraccas (where it lasted seven hours 

 without any movement of the ground), and also in Hayti, 

 in Jamaica, and near the Lake of Nicaragua. 



These phenomena of sound, even when unaccompanied 

 by sensible shocks, produce a peculiarly deep impres- 

 sion, even on those who have long dwelt on ground 

 subject to frequent trembling. One awaits with anxiety 

 that which is to follow the subterranean thunder. \ The 

 most striking instance of uninterrupted subterranean 

 noise, unaccompanied by any trace of earthquake, is the 

 phenomenon which is known in the Mexican territory by 

 the name of "the subterranean roaring and thundering, 

 (bramidos y truenos subterraneos) of Guanaxuato." ( 18 ?) 

 This rich and celebrated mountain city is situated at a dis- 

 tance from any active volcano. The noise began on the 9th 

 of January, 1784, at midnight, and lasted above a month. 

 I have been enabled to give a circumstantial description of 

 the phenomenon from the report of many witnesses, and 

 from the documents of the municipality, which I was per- 

 mitted to make use of. Prom the 13th to the l-6th of 

 January, it was as if there were heavy storm clouds under 

 the feet of the inhabitants, in which slow rolling thunder 

 alternated with short thunder- claps. The noise ceased gra- 

 dually, as it had commenced ; it was confined to a small space, 

 for it was not heard in a basaltic district at the distance 



