348 AGE OF THE EARTH AS AN ABODE FITTED FOR LIFE. 



denser tliau the glass produced by quick freezing of the liquid. lie 

 gives no data, nor do Eiicker and Eoberts- Austen, who have also experi- 

 mented on the thermodynamic properties of melted basalt, give any 

 data as to the latent heat evolved in the consolidation of liquid lava 

 into rock of basaltic quality. Guessing it as three times the latent heat 

 of fusion of the diabase pitchstone, I estimate a million cubic centime- 

 ters of liquid frozen per square centimeter per centimeter per three 

 years. This would diminish the depth of the liquid at the rate of a 

 million centimeters per three years, or 40 kilometers in twelve years. 



25. Let us now consider in what manner this diminution of depth of 

 the lava ocean must have proceeded by the freezing of portions of it; 

 all having been at temperatures very little below the assumed 1,420^ 

 melting temperature of the bottom when the depth was 40 kilometers. 

 The loss of heat from the white-hot surface (temperatures from 1,420° to 

 perhaps 1,380° in different parts), at our assumed rate of 2 (gram- 

 water centigrade) thermal units per square centimeter per second pro- 

 duces very rapid cooling of the liquid within a few centimeters of the 

 surface (thermal capacity 0.36 per gram, according to Barus), and in 

 consequence great downward rushes of this cooled liquid and upward 

 of hot liquid, spreading out horizontally in all directions when it reaches 

 the surface. When the sinking liquid gets within perhaps 20 or 10 or 5 

 kilometers of the bottom, its temperature^ becomes the freezing point 

 as raised by the increased pressure; or, perhaps more correctly stated, 

 a temperature at which some of its ingredients crystallize out of it. 

 Hence, beginning a few kilometers above the bottom, we have a snow 

 shower of solidified lava or of crystalline flakes, or prisms, or granules 

 of feldspar, mica, hornblende, quartz, and other ingredients; each little 

 crystal gaining mass and falling somewhat faster than the descending 

 liquid around it till it reaches the bottom. This process goes on until, 

 by the heaping of granules and crystals on the bottom, our lava ocean 

 becomes silted up to the surface. 



PROBABLE ORIGIN OF QRANITE. 



26. Upon the suppositions we have hitherto made we have, at the 

 stage now reached, all round the earth at the same time a red-hot or 

 white-hot surface of solid granules or crystals, with interstices filled by 

 the mother liquor still liquid, but ready to freeze with the slightest 

 cooling. The thermal conductivity of this heterogeneous mass, even 

 before the freezing of the liquid part, is x)robably nearly the same as 

 that of ordinary solid granite or basalt at a red heat, which is almost 

 certainly^ somewhat less than the thermal conductivity of igneous 

 rocks at ordinary temperatures. If you wish to see for yourselves how 



1 The temperature of the sinking liquid rock rises in virtue of the increasing pres- 

 sure; but much less than does the freeziug point of the liquid or of some of its 

 ingredients. (See Kelvin Math, and Phys. Papers, Vol. Ill, pages 69, 70.) 



2 Proc. R. S., May 30, 1895. 



