76 
CAUSES OF GEOLOGICAL CHANGES. 
sixty feet in height, flowed over land lying beyond the reach of 
the highest tides. In the case oj the quay there was an evident 
subsidence of the land. Other recent examples of the same ef¬ 
fect of earthquakes are recorded at Port Royal, in Jamaica, in the 
Delta of the Indus, and at Puzzuoli, near Naples. The opposite 
effect of elevation has been witnessed at Puzzuoli, and on the 
coast of Chili, near Valparaiso. This double agency of earth¬ 
quakes in producing a movement both upwards and downwards, 
is a fact of great importance in the science of geology. 
The effects of an earthquake are seldom confined to the spot 
where the greatest force is exerted. That which destroyed Lis¬ 
bon was felt to the extremities of the continent of Europe. The 
movement of the earth in this instance is said to liave been undu- 
latory, and the undulation to have travelled at the rate of twenty 
miles in a minute. Where no shock was experienced the water 
of springs, lakes, and rivers was strangely affected, becoming tur¬ 
bid and overflowing its hanks without any apparent cause. Along 
the nothern coast of Africa the effects were hardly less disastrous 
than in Portugal itself. 
Having stated some of the more remarkable phenomena of both 
volcanoes and earthquakes, we are prepared to observe that there 
is such a connexion between tlie two that we shall be safe in re¬ 
ferring them to the same common cause. It might perhaps be 
sufficient to state in proof of this that those counties in which there 
are burning mountains, are beyond all others vexed by earthquakes. 
Soutliern Italy and Chili, may be cited as examples. In the pro¬ 
vince of Calabria, not less than nine hundred and forty-nine distinct 
shocks were felt in a single year—1783. The Atlantic States 
being far removed from the seat of any active volcano are seldom 
visited by these terrible movements of the stony strata of the 
globe. But we have more direct and positive evidence of the 
connexion between earthquakes and volcanoes. It has been alrea¬ 
dy stated that an eruption of a volcano, that has been for some time 
dormant is commonly attended by convulsions in the country around 
it. It appears farther that there is a subterraneous communication 
and sympathy not only between different districts of a country con- 
tigous to the same volcano, but also between craters that are far 
distant from each other, so that an eruption in one part of the 
globe will be attended by disturbances in a region many miles, 
and sometimes many degrees distant. “The volcano of Pasto in 
South America, uninterruptedly vomited a high column of smoke 
during three months of the year 1797, and this column disappeared 
at the very moment when at the distance of nearly three hundred 
miles the great earthquake of Riobamba, and the mud eruption 
of the Moya, killed from thirty to forty thousand Indians. The 
sudden appearance of a new island, thrown up by volcanic fires, 
amongst the Azores, on the 30th of January ISl), was the fore¬ 
runner of those dreadful shocks which further to the west shook 
almost uninterruptedly from the month of May ISll, to that of 
