164 Scientific Intelligence. 



"Probable Origin of Basaltic Hock* — § 28. We have hitherto 

 left, without much consideration, the mother liquor among the 

 crystalline granules at all depths below the bottom of our shoal- 

 ing lava ocean. It was probably this interstitial mother liquor 

 that was destined to form the basaltic rock of future geological 

 time. Whatever be the shapes and sizes of the solid grauules 

 when first falling to the bottom, they must have lain in loose 

 heaps with a somewhat large proportion of space occupied by 

 liquid among them. But, at considerable distances down in the 

 heap, the weight of the superincumbent granules must tend to 

 crush corners and edges into fine powder. If the snow shower 

 had taken place in air we may feel pretty sure (even with the 

 slight knowledge which we have of the hardness of the crystals 

 of feldspar, mica and hornblende, and of the solid granules of 

 quartz) that, at a depth of 10 kilometers, enough of matter from 

 the corners and edges of the granules of different kinds, would 

 have been crushed into powder of various degrees of fineness, to 

 leave an exceedingly small proportionate volume of air in the in- 

 terstices between the solid fragments. But in reality the effect- 

 ive weight of each solid particle, buoyed as it was by hydrostatic 

 pressure of a liquid less dense than itself by not more than 20 or 

 15 or 10 per cent, cannot have been more than from about one- 

 fifth to one-tenth of its weight in air, and therefore the same de- 

 gree of crushing effect as would have been experienced at 10 

 kilometers with air in the interstices, must have been experienced 

 only at depths of from 50 to 100 kilometers below the level of 

 the lava ocean." 



" § 29. A result of this tremendous crushing together of the 

 solid granules must have been to press out the liquid from among 

 them, as water from a sponge, and cause it to pass upwards 

 through the less and less closely packed heaps of solid particles, 

 and out into the lava ocean above the heap. But, on account of 



* Note by the Editor: An Addendum at the close of the paper quotes the 

 following determination of melting points by Prof. Roberts- Austen: 



Melting-point. Error. 



Feldspar 1520° C. ±30° 



Hornblende about 1400° 



Mica 1440° ±30° 



Quartz 1775° ±15° 



Basalt about 880° 



The author adds : 



"These results are in conformity with what I have said in §§ 26-28 on the 

 probable origin of granite and basalt, as they show that basalt melts at a much 

 lower temperature than feldspar, hornblende, mica, or quartz, the crystalline in- 

 gredients of granite. In the electrolytic process for producing aluminium, now 

 practised by the British Aluminium Company at their Foyers works, alumina, of 

 which the melting-point is certainly above 1700° C. or 1800° C , is dissolved in a 

 bath of melted cryolite at a temperature of about 800° C. So we may imagine 

 melted basalt to be a solvent for feldspar, hornblende, mica, and quartz at tem- 

 peratures much below their own separate melting-points; and we can understand 

 how the basaltic rocks of the earth may have resulted from the solidification of 

 the mother liquor from which the crystalline ingredients of granite have been 

 deposited." 



