43 o 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 tol- 

 erably certain that the granite was formed under peculiar circum- 

 stances ; 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 sub- 

 stances, and subjected to enormous pressure. What the original con- 

 dition 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 ex- 

 posed by denudation, etc. ; their origin was deep in the central por- 

 tions of ancient volcanoes, where, by partial melting and slow cooling, 

 under intense pressure, and in the presence of some water, the va- 

 rious minerals came together and crystallized into granite. Science- 

 Gossip. 



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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 consid- 

 ered absolutely, of unparalleled value; that the period since Watt's 



