
Parr i.Secr.ii] EARTHQUAKES. — 271 
miles deep; while that of Herzogenrath in 1873 was placed by Von 
_ Lasaulx at a depth of about 143 miles.’, 
Geological Effects——These are dependent not only on the 
_. strength of the concussion but on the structure of the ground, and on 
the site of the disturbance, whether underneath land or sea. They 
include changes superinduced on the surface of the land, on terrestrial 
and oceanic waters, and on the relative levels of land and sea. 
1. Effects upon the Soil and General Surface of a 
Country.—tThe earth-wave or wave of shock underneath a country 
may traverse a wide region and affect it violently at the time without 
leaving permanent traces of its passage. Blocks of rock, however, 
already disengaged from their parent masses, may be rolled down 
into the valleys below. Landslips are produced, which may give 
rise to considerable subsequent changes of drainage. In some 
instances the surfaces of solid rocks are shattered as if by gunpowder, 
as was particularly noticed in the Concepcion earthquake of 1835 to 
have taken place among the Primary rocks of that district.2 It 
has often been observed also that the soil is rent by fissures which 
vary in size from mere cracks, like those due to desiccation, up to 
deep and wide chasms. Permanent modifications of the landscape 
may thus be produced. Trees are thrown down and buried, wholly 
or inpart,inthe rents. These superficial effects may, indeed, be soon 
effaced by the levelling power of the atmosphere. Where, however, 
the chasms are wide and deep enough to intercept rivulets, or to 
serve as channels for heavy rain-torrents, they are sometimes further 
excavated, so as to become gradually enlarged into ravines and valleys, 
as has happened in the case of rents caused by the earthquakes of 
1811-12, in the Mississippi valley. Asa rule, each rent is only a few 
-yards long. Sometimes it may extend for half a mile or even more. 
In the earthquake which shook the South Island of New Zealand in 
1848, a fissure was formed, averaging 18 inches in width and traceable 
for a distance of 60 miles parallel to the axis of the adjacent moun- 
tain-chain. The subsequent earthquake of 1855, in the same region, 
gave rise to a fracture which could be traced along the base of a 
line of cliff for a distance of about 90 miles. Dr. Oldham has 
_ described a remarkable series of fissurings which ran parallel with 
the river of Calhar, Eastern British India, varying with it to every 
point of the compass and traceable for 100 miles.’ 
Remarkable circular cavities have been noticed in Calabria and 
elsewhere, formed in the ground during the passage of the earth- 
wave. In many cases these holes serve as funnels of escape for 
an abundant discharge of water, so that when the disturbance ceases 
they appear as pools. ‘They are believed to be caused by the sudden 
collapse of subterranean water-channels and the consequent forcible 
ejection of the water to the surface. 
1 Hofer, Sitzb. Akad. Wien, December 1876. Von Lasaulx, Das Erdbeben von 
Herzogenrath am 22 October, 1873, Bonn, 1874. . 
2 Darwin, Journal of Researches, 1845, p. 303. 
3 Q. J. Geol. Soc. xxviii. p. 257, 
