204 
ELEVATION OP LAND. 
" In order," says Mr. Lyell, " to give some idea 
of the enormous amount of change which this con- 
vulsion may have occasioned, let us assume that 
the extent of country moved was correctly esti- 
mated at 100,000 square miles; an extent just equal 
to half the area of France, or about five sixths of 
the area of Great Britain and Ireland. If we sup- 
pose the elevation to have been only three feet, on 
an average, it will be seen that the mass of rock 
added to the continent of America by the move- 
ment, or, in other words, the mass previously be- 
low the level of the sea, and, after the shocks, per- 
manently above it, must have contained 57 cubic 
miles in bulk (or about as high as iEtna), with a cir- 
cumference at the base of nearly 33 miles." Mr. 
Lyell calculates that the mass of rock elevated must 
have been, if two miles thick, 200,000 cubic miles 
in length, and have exceeded in weight 363 million 
of the great pyramids of Egypt. 
In the year 1819 a violent earthquake was expe- 
rienced at Cutch, in the Delta of the Indus, which 
caused the sea to rush in by the Eastern mouth of 
the Indus, and convert a tract of land 2000 square 
miles in area into an inland sea. At the same time, 
also, a tract of country 50 miles in length and 16 
in breadth was elevated 10 feet, comprising an area 
of 7000 square miles, equal to about one fourth of * 
Ireland. 
The motion of the ground produced by earth- 
quakes is not always the same ; sometimes resem- 
bling the undulating motion of a heavy swell at sea, 
though much quicker, and being at others tremu^ 
lous, as if some force shook the earth violently in 
one spot. The former of these is far more danger- 
ous, as it forces walls and buildings off their centres 
of gravity, crushing whatever maybe beneath them. 
Earthquakes not only cause an elevation, but 
also a subsidence of the land. Thus, in the year 
541,Pompeiopolis was swallowed up; in 867, Mount 
