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that seismic activity was due to faulting of strata chiefly in 
regions where recent secular upheavals have occurred and where 
the gradients are very steep (so-called ‘‘ monoclinal folding’”’). 
The supporters of this theory state that steam explosions may 
cause some (but only a few) of the milder earthquakes, but that 
it is inconceivable that such tremendous effects and these spread 
over such large areas could be produced by the agency of sub- 
terranean steam only. Mr. Hora thought that the weakness of 
this latter theory consisted in the fact that faulting and disloca- 
tions of strata seemed symptoms only of some still more mighty 
forces at work within the earth’s crust, and such forces its 
supporters maintained were due to secular contraction —a theory 
which, as stated above, was hardly tenable in the light of modern 
researches. 
The lecture was concluded by a few remarks on submarine 
volcanoes and bradyseismic movements. As regards the former 
a slide was shown of a typical submarine eruption as it appeared 
at sea, and the lecturer remarked that they were very common 
indeed, almost as common as terrestrial eruptions. He then 
showed a slide of the remarkable island which rose from the 
Mediterranean Sea in 1831 and remained in existence only three 
weeks,—it was known as ‘‘Graham’s Island,’ and evidently 
resulted from a submarine eruption. To illustrate bradyseismic 
movements, Mr. Hora showed a woodcut of the celebrated 
remains of the temple of “Jupiter Serapis” on the coast of 
Italy, and explained that there must have been at least five 
alternate subsidences and elevations within the last 2,000 years. 
Darwin’s coral reef theory afforded a splendid example of 
slow subsidence of the ocean bed, and a slide was shown to 
illustrate the three stages of a coral reef’s evolution. Having 
explained that corals could only live in salt water at a tempera- 
ture never below 68° F., nor at a depth greater than 90ft. from 
the sea surface, the question arose—“ How came it that numerous 
coral islands lie studded in groups in all the great oceans, 
especially the South Pacific?” Darwin suggested that a 
‘‘ fringing ’’ reef was first formed near some island and this by 
subsidence was converted into a ‘‘barrier’’ reef, and when the 
island disappeared altogether by further subsidence an ‘atoll ”’ 
or ring of coral only remained, hence the atoll was the tomb- 
stone of a departed island. This theory, despite the attacks 
made upon it by Agassiz, Sir John Murray, and other naturalists, 
had been verified by borings made recently at Funafuti, and 
although there was evidence now that some coral reefs had arisen 
by deposition on submarine volcanoes or on shore platforms or 
submarine flats formed by the erosion of pre-existing land 
surfaces, and not by subsidence, still a large number of them 
certainly came into existence in the way that Darwin had 
suggested. 
