28 REPORT—1850. 
earthquakes do not appear to be those whose theatre of action 
is closest to the volcanic vents themselves: on the contrary, 
the most violent recorded earthquakes appear to have con- 
vulsed regions lying some degrees away from the nearest 
volcano in action. 
10th. And in general the most violent recorded earthquakes 
have occurred within a certain undetermined radius round 
active volcanic centres, not far inland or in the heart of con- 
tinents, but upon the sea-coasts, or near them. 
Some doubt however hangs over this last, as some very ancient earthquakes 
of tremendous intensity appear to have occurred in central and northern Asia. 
Whether the proximity of the sea also is directly concerned or not is unde- 
termined: it seems probable that all the great lines or centres of active vol- 
canic action are near the sea-coast, and that their propinquity determines that 
of the earthquake. 
10th dis. It seems to be the opinion of Humboldt, that the area 
of shaken country also sometimes enlarges in consequence of 
a previous violent earthquake. 
Thus, “It is only since the destruction of Cumana in 1797, that every 
shock of the southern coast is felt in the mica-slate of the peninsula of Ma- 
niguarez.’—(Cosmos.) The centre of disturbance also shifts its position 
during long-continued earthquakes. Thus, in the Calabrian earthquake it 
moved twice northward eight or nine leagues, and in the New Madrid earth- 
quakes of 1811 to 1813, the progress northward in the basins of the Mis- 
sissippi, the Ohio and the Arkansas was remarked. 
This opinion, however, is hard to give unquestioned credence to, if we 
bear in mind that earthquake shocks are not communicated through tubes or 
vents, torn in any way or already existing under ground, but are best pro- 
pagated and go furthest where the ground through which they pass is most 
solid, dense and homogeneous. 
11th. Earthquake shocks have been felt on the ocean at vast 
distances from any land, and in some cases the shock has been 
nearly vertical and occurring in places where the depth of 
water was profound, and where no phznomenon on the sur- 
face of the ocean indicated any volcanic action then active 
beneath. 
On this we may remark, however, that the most formidable volcanic ac- 
tivity, greater probably than we have any experience of on the dry land, may 
possibly exist constantly or occasionally in the bed of the deep ocean, and 
yet no trace of it beyond a transient earthquake shock be known to those 
floating over the surface. At a depth of five miles of sea water we can well 
imagine that lava poured out would be rapidly cooled, that steam formed 
would be condensed long before it reached the surface, that rocks projected 
upwards into so dense a resisting medium would fall back long before they 
reached even the sun’s light, and that pumice or other light and porous pro- 
ducts of volcanoes on land or in shallow water may have no existence under 
such prodigious pressure. 
Great confusion prevails amongst earthquake narrators as to the use of the 
word shock. We find constant mention made of the “shock lasting several 
