44 REPORT—1850. 
its rate will be about 4700 feet per second, and in air about 1140, and at 
the following rates for the rocks or formations, given below :— 
Lias limestone .. ........ ..3640 feet per second. 
Coal-measure sandstone ....5248 Ἔ 
Oolite: sale δὲ te inv εἶν aadldoor 5723 a 
Primary limestone......... . 6696 i 
Carboniferous limestone .... 7075 
Hardslates;. cnet. ii Ὁ τοί suv 12757 ” 
For granite and igneous rocks we have as yet no data, but the rate will be 
greater than in any of the preceding. 
Another remarkable fact observed as to sound is, that in some great earth- 
quakes sounds have continued to be produced at comparatively regular 
intervals for long periods after the shock, but unaccompanied with any sen- 
sible motion of the ground. Boussingault informs us, that, after the earth- 
quake of New Granada in 1827, noises like the discharge of cannon were 
heard in the whole of the valley ef Cauca fora long period, at nearly regular 
intervals of thirty seconds, and several other instances of the same sort are 
recorded ; these, like the slight noises in Perthshire at present, I should be 
disposed to attribute to the periodic fracturing in cooling of newly-formed 
igneous rock below or near the country where they are heard. 
As there are shocks of earthquakes without any sound, so there are sub- 
terraneous sounds heard often without any shocks. Thus in Caraccas, on 
the plains of Calabozo, and on the banks of the Apure, a branch of the 
Orinoco, over a region of 9200 square miles, Humboldt informs us there was 
heard on the 30th of April 1812 an extraordinary thundering noise without any 
shock, while the voleano of St. Vincent, in the Lesser Antilles, at a distance 
of 632 miles to N.E., was pouring out lava; this, he adds, was as if an erup- 
tion of Vesuvius was heard in the south of France, In the great eruption of 
Cotopaxi in 1744, subterraneous noises like those of cannon were heard in 
Honda on the Magdelana River. The crater of Cotopaxi is 18,000 feet 
above Honda, and separated from it by the colossal mountain chain of Quito, 
Pasto and Popayan, full of valleys and rents, and in distance 436 miles apart. 
The sound. he says, was certainly not propagated through the air, but through 
the earth, and at a great depth. During the violent earthquake of New ὦ 
Granada of Feb. 1835, subterraneous thunder was simultaneously heard at 
Popayan, Bagota, Santa Marta, and Caraccas (where it continued for seven 
hours without any movement of the ground); also in Hayti, Jamaica, and on 
the lake of Nicaragua. 
The subterraneous noises of Mexico, which continued without any trace 
of earthquake at Guanaxuato, for more than a month from midnight of Janu- 
ary 9, 1784, and are known there as the bramidos y truenos subterraneos, 
described as if thuuder-clouds lay beneath the feet of the inhabitants, from 
which issued slow rolling sounds and short quick claps of thunder,—belong to 
this order also ; and there can be little doubt but that Pliny formed his notion 
of earthquake theory from such sounds, when he says, “ Neque aliud est in terra 
tremor, quam in nube tonitrum, nee hiatus aliud quam cum fulmen erumpit, 
incluso spiritu luctante et ad libertatem exire nitente.”—Plin. lib. ii. 79. 
After recording many of these singular phenomena, Humboldt (‘ Cosmos’) 
sums up oddly enough in these words :—‘“ Thus do chasms in the interior of 
the earth open and close, and the sonorous waves either reach us or are in- 
terrupted in their progress,’—apparently forgetting for the moment that the 
sounds must be conveyed more surely and more rapidly through the solid 
crust of the earth than through any fissure. These sounds, without shock, 
must be attributed to impulses given in such directions, and with such a re- — 
