68 
CAUSES OP GEOLOGICAL CHANGES. 
said to have been produced by the accumulation of sand and other 
causes. 
Most of the low islands of the Pacific are supposed to own their 
existence to the labours of the Zoophytes. A generation of these 
animalcules, planted by means that are unknown to us, occupies 
with a colony a certain extent of surface; probably the tops of a 
mountain at the bottom of the sea—in some cases at least, the 
circular edge of the crater of a submarine volcano. After having 
lived out the natural term of its existence it perishes, leaving its 
habitations behind. The material of which they are built is car¬ 
bonate of lime, with a very small quantity of animal matter asso¬ 
ciated with it. On the top of the layer of coral thus produced, 
a second generation comes into being, and shares the fate of its 
predecessor. Others succeed, until at length an imnjense column 
is raised in the sea, its top being larger than its base, and its height 
from fifty to one hundred feet. When they have brought this pro¬ 
duct of their labours to the level of low water mark, new genera¬ 
tions cease to be produced upon its top. To be constantly covered 
with water seems to be indispensable to their existence. “But 
“the sand,pieces of coral, and other broken fragments thrown up 
“by the sea, adhere to the rock and form a.solid mass upon it as 
“high as the common tides reach. That elevation surpassed, 
“the future remnants being rarely cov^ered, lose their adhesive 
“property, and remaining in a loose state, form what is usually 
“called a key upon the top of the reef. The new bank is not 
“long in being visited by sea birds, salt plants take root upon it, 
“and a soil begins to be formed; a cocoa-nut or the drupe of a pan- 
“danus is thrown on shore; land birds visit it and deposit the seeds 
“of shrubs and trees; every high tide, and still more every gale, 
“adds something to the bank, the form of an island is gradually 
“assumed, and last of all comes man to take possession.” 
And a wet uncomfortable time he would have of it unquestio¬ 
nably. The case furnishes another example of those rash infer¬ 
ences from'premises which do not warrant the conclusions that 
are drawn from them, which are unfortunately not yet altogether 
banished from the science of geology. It is very evident that the 
weaves cannot, unaided and alone, throw up an island over which 
they will not continue to break during every violent storm. 
It is quite certain that the coral reefs traversing those seas, have 
been created in the manner supposed. It is further certain that 
before becoming tiie habitation and dwelling place of man, they 
must, in all cases, have been placed beyond the reach of the 
w'aves; either by a depression of the general level of the ocean, 
or by being lifted out of its bed by a force acting from below. 
And after having studied the effects of volcanic action in other 
parts of the globe, we shall become satisfied that it has in all 
cases been conjoined with the labours of the Zoophytes in the 
production of the coral islands of the Pacific. 
