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of Edinburgh , Session 1867-68. 
are lined with crystals in point of composition much simpler than 
the matrix, or even consisting of a single element only, and yet 
deriving their ingredient or ingredients from the matrix — such 
being a law generally of crystallisation from composite mixtures in 
a state of fusion or of solution. We should moreover expect to find 
where the melted matter itself of subterranean fire has burst up- 
wards through the stratiform rocks, that it carried broken masses of 
these rocks along with it, and on cooling showed them included in 
the invading and now concreted liquid. We should see the dis- 
rupting liquid mass diffusing itself in veins in every direction 
through the shattered beds, and even insinuating itself between 
the beds, separating them from each other, and now itself forming 
beds betwixt them. We might also expect to see in the huge 
masses of subterraneous matter which had been thrown up in a 
melted state, that, by virtue of their perfect fusion and very slow 
cooling, they now present us with the most crystalline texture of 
all rocks, show even a separation into crystalline bodies totally dif- 
ferent from one another in composition, and display, in accidental 
cavities in their interior, lining crystals of the most perfect form, 
and of the simplest materials which the matrix of rock can yield. 
Now, all the phenomena thus described, as it were by anticipa- 
tion, we do actually witness on examining carefully the several 
rocky beds and masses which form the present crust of our earth. 
Therefore there can be no doubt that this crust has been formed 
from the crumbling of a more ancient dry land, deposited in the 
sea, and afterwards fused and raised above the sea by the agency of 
subterranean fire. 
Such is in brief terms a summary of the main points and proofs 
of Hutton’s theory, beautifully but tersely set forth in his own 
dissertation in our Transactions. I might have taken this sum- 
mary from the admirable extension and illumination of the theory 
in the classical work of his pupil and friend, Professor Playfair, 
“ The Illustrations of the Huttonian Theory of the Earth ; ” but I 
have preferred to use for the purpose Hutton’s own exposition, 
because, though he has often been called obscure, I cannot find 
obscurity anywhere when he is read with the light of details since 
acquired to science, and probably not altogether unknown to him, 
notwithstanding that for brevity’s sake he has not put them forward. 
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