52 REPORT—1850. 
of hard and elastic rocks, vast crevasses may be rent into the mountain 
masses, huge blocks may be detached at the instant of the shock (as at 
Messina, and as seen from the deck of the Volage, when a mighty cliff de- 
tached itself, and plunging at once into deep water disappeared), and may 
fall into the valleys, and be shattered into fragments, vast, angular and with- 
out order, such as we see filling the commencement of the pass of the 
Spliichen above Chiavenna. But the mountain torrents still find their way 
through or over such debris, the dams formed are not water-tight, their ma- 
terials are too huge, and interlock too much, to be moved by debacle any 
great distances; the whole iron frame of the country is too elastic and too 
strong to be very greatly altered, and the earthquake leaves but compara- 
tively slight traces of its destroying hand, save upon the frail habitations of 
man, and upen his best and largest works. 
Ath. Fissures of various sizes are formed in the earth’s crust. 
These are directly formed in the solid rock. Sir Hans Sloane describes the 
rocks in the Blue Mountains of Jamaica as greatly shattered in 1687 by the 
earthquake. 
Mrs. Graham describes the granite rock of the beach at the promontory 
of Quintero in Chili, after the earthquake of 1822, as found rent by sharp 
recent clefts, very distinguishable from the older ones, bué running in the 
same direction. Many of these could be traced to a distance of a mile and a 
half across the neighbouring promontory, where in some instances the earth 
parted, and left the base of the hill exposed. (Geol. Trans., vol. i. 2nd series, 
p. 415. 
Hot eee frequently are found issuing from such clefts in igneous rock. 
Thus Humboldt tells us that the ‘‘ Aguas calientes de las Trincheras burst 
out from a granite rock, split into regular fragments” (Cosmos); and many 
other similar instances may be found recorded. 
Most, if not all writers on this subject have tacitly assumed however that 
all fissures formed during earthquakes are due to the direct action of the 
shock ; and some accounts, such as that of the great Jamaica earthquake of — 
1692, affirmed “ that the ground undulated like a rolling sea, and that fissures 
opened as the undulations passed, two or three hundred of which might be 
seen open at once; that these opened and closed again rapidly, as the un- — 
dulation rose and fell; and that people were even caught and bitten in two 
by these Titanic mouths ; that some, thus swallowed up, were again cast out.” 
Assuming this narrative veracious, I for some time believed the opening © 
and closing of fissures by the direct passage of the earth-wave to be possible — 
in incoherent formations. On further consideration of the subject, however, — 
I am disposed to reject this solitary and truly wonderful Jamaica narrative, 
for the present at least; and judging from a connected view of all the other 
narratives of earthquakes, to state my strong impression, that fissures, at least 
those of any magnitude, any that are more than rents or cracks in rock or 
masonry or other coherent bodies, are never produced during earthquakes 
directly by the transit of the shock, but are solely the result of secondary — 
actions, and due either— - 
1. To landslips, more or less complete. 
2. To subsidences in the ground, due to subterranean action at great 
depths, of the true elevatory and depressory character, and producing 
lateral slips by resolution of motion. 
8. To elevations of the ground produced in the same way, and producing 
similar effects. ᾿ 
4, To the action of water, either forced up from beneath, or removing 
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