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Geology of Sydney. 
One often heats the question asked, “How did 
these great boulders get up there?” More than once 
the writer has been assured that nothing but an earth- 
quake could do it, ray informant seemingly forgetting 
that an earthquake would more probably bring those 
great rocks down than throw them up to their hardly 
stable positions. Popularly, earthquakes have taken 
a firm hold in this direction — a fact worth noting 
when it is borne in mind that the presence of these 
delicately-poised boulders is the very best proof that 
Australia has not for long ages past been subjected to 
any violent earth movements. 
It is interesting, however, to follow the explana- 
tion that geologists give as to the origin of granite 
boulders crowning the summits of mountains. The 
boulders are simply the harder portions of the granite, 
which remain when the softer portions of the rock 
have disintegrated and decomposed. The resulting 
fine materials are removed by rain and running 
water. But it will be asked, “ Does granite, then, 
decompose so readily?” No doubt about it. Granite 
seen in polished slabs may appear “more lasting than 
brass;” but it is, in truth, liable to disease and decay. 
In many parts of the world vast areas of granite have 
been disintegrated, through a predisposition on the 
part of its felspars to alter into kaolin. The granites 
of Auvergne in Central Prance are examples of this 
seeming mysterious decay, which has been happily 
called by Dolomieu “ la maladie du granite .” 
But we need not go abroad for examples of this 
