80 Lord Kelvin on the Age of the 



Probable Origin of Basaltic Bock * (§§ 28, 29.) 



§ 28. We have hitherto left, without much consideration, 

 the mother liquor among the crystalline granules at all 

 depths below the bottom of our shoaling lava ocean. It was 

 probably this interstitial mother liquor that was destined 

 to form the basaltic rock of future geological time. What- 

 ever be the shapes and sizes of the solid granules 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 hard- 

 nesses of the crystals of felspar, mica and hornblende, and 

 of the solid granules of quartz) that, at a depth of 10 kilo- 

 metres, 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 exceed- 

 ingly small proportionate volume of air in the interstices 

 between the solid fragments. But in reality the effective 

 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 there- 

 fore the same degree of crushing effect as would have been 

 experienced at 10 kilometres with air in the interstices, must 

 have been experienced only at depths of from 50 to 100 kilo- 

 metres below the bottom 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 the great resistance against the liquid 

 permeating upwards 30 or 40 kilometres through interstices 

 among the solid granules, this process must have gone on 

 somewhat slowly ; and, during all the time of the shoaling of 

 the larva ocean, there may have been a considerable proportion 

 of the whole volume occupied by the mother liquor among 

 the solid granules, down to even as low as 50 or 100 kilo- 

 metres below the top of the heap, or bottom of the ocean, at 



* See Addendum at end of Lecture, 



