Page:Popular Science Monthly Volume 9.djvu/454

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THE POPULAR SCIENCE MONTHLY.

would have been seen in definite crystalline form, and its crystals would have interfered with and penetrated those of the other mineral constituents of the rock. Again, if we look carefully at the quartz with a moderately high power, we shall see in it certain small cavities, and some of these will be seen to contain a certain amount of liquid, and also an air-bubble, which will move as the specimen is moved. This liquid has been proved to be water, and from the fact of its not entirely filling the cavity we learn that a reduction of temperature has taken place since the water was first caught up by the quartz, causing the contents of the cavities to contract. Sometimes we shall find other cavities, which, instead of containing water, contain small crystals, or even air only. Now, from all these facts it appears tolerably certain that the granite was formed under peculiar circumstances; it has never been such a purely molten rock as is the lava of a volcano, which is poured out from its crater to the light of day. We gather that it was rather formed at great depths in the earth, where it may have been partially melted, partially subjected to the action both of water and of steam, charged with various mineral substances, and subjected to enormous pressure. What the original condition of granite was we cannot tell; some have gone so far as to think that it may have been that of a sedimentary rock, which has been metamorphosed by the forces just alluded to. But, whatever the primary state of granite may have been, its present condition shows it to belong undoubtedly to the igneous class of rocks, but to have been formed under conditions differing from those which have given rise to lavas reaching the surface. As far as can be gathered, the granite rocks, as such, have never seen the light of day until exposed by denudation, etc.; their origin was deep in the central portions of ancient volcanoes, where, by partial melting and slow cooling, under intense pressure, and in the presence of some water, the various minerals came together and crystallized into granite.—Science-Gossip.

 

THE APOTHEOSIS OF STEAM.
By JOHN S. HITTELL.

IN a newspaper notice of a late book the critic complains that it is "an apotheosis of steam," an offense which he does not explain, but he conveys the inference that the book mentioned attributes to steam and to its age too much influence and importance in human life. He raises the question whether steam deserves apotheosis, and I answer affirmatively, undertaking to prove that, with its associate forces, it has conferred upon mankind benefits of vast, and, if considered absolutely, of unparalleled value; that the period since Watt's