May 19, 1899.] 



SCIENCE. 



705 



all solid, a little distance down ; becoming 

 thicker and thicker very rapidly at first ; 

 and after a few weeks certainly cold 

 enough at its outer surface to be touched 

 by the hand. 



PROBABLE ORIGIN OF BASALTIC ROCK.* 



§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 inter- 

 stitial mother liquor that was destined to 

 form the basaltic rock of futui-e geological 

 time. Whatever be the shajjes 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 hardnesses 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 dif- 

 ferent kinds, would have been crushed into 

 powder of various degrees of fineness, to 

 leave an exceedingly small proportionate 

 volume of air in the interstices between the 

 solid fragments. But in reality the effec- 

 tive 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 degree of crushing eifect as would 

 have been experienced at 10 kilometers 

 with air in the interstices, must have been 



*See Addendum at end of Lecture. 



experienced only at depths of from 50 to 

 100 kilometers below the bottom of the lava 

 ocean. 



§ 29. A result of this tremendous crush- 

 ing 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 kilometers through interstices among 

 the solid granules, this process must have 

 gone on somewhat slowly ; and, dui-ing all 

 the time of the shoaling of the lava ocean, 

 there may have been a considerable pro- 

 portion of the whole volume occupied by 

 the mother liquor among the solid granules, 

 down to even as low as 50 or 100 kilo- 

 meters below the top of the heap, or bottom 

 of the ocean, at each instant. When con- 

 solidation reached the surface, the oozing 

 upwards of the mother liquor must have 

 been still going on to some degree. Thus, 

 probably for a few years after the first con- 

 solidation at the surface, not probably for 

 as long as one hundred years, the settle- 

 ment of the solid structure by mere me- 

 chanical crushing of the corners and edges 

 of solid granules, may have continued to 

 cause the oozing upwards of mother liquor 

 to the surface through cracks in the first 

 formed granite crust and through fresh 

 cracks in basaltic crust subsequently formed 

 above it. 



Leibnitz's consistentior status. 



§ 30. When this oozing everywhere 

 through fine cracks in the surface ceases, 

 we have reached Leibnitz's consistentior 

 status; beginning with the surface cool 

 and permanently solid and the tempera- 

 ture increasing to 1150° C. at 25 or 50 or 

 100 meters below the surface. 



