1899.] SCIENCE. 97
ical time, which was based on the assumption of a solid earth, and he shows that it is necessary to assume solidity, not only as a present con- dition) but as one that existed from the beginning of the period to which the estimates relate ; and this cannot be admitted.
It has been taken too much for granted that in early geological times the subaerial forces operated with much greater energy than at present. But Sir Archibald Geikie has pointed out that in the early sedimentary registers of the earth's history not only is there no evidence of colossal floods, tides and denudation, but there is incontrovertible proof of con- tinuous orderly deposition. The ancient Torridon sandstones of North- west Scotland reveal pebbles gently laid down, with fine sand sifted in between them, for mile after mile across the Highland mountains and glens.
Professor Bonney has made an examination of the parent rock of the South African diamond. A critical point was reached by the discovery of diamonds embedded in boulders of garnet or eclogite. As these boulders are truly water-worn, it would appear that whilst the rock of which they are composed may itself be the birthplace of the diamond, they are certainly present in the "blue ground" only as a derivative from older formations.
An investigation by Mr. Phillips into the natural gas that escapes from the earth in the Pittsburg district of the United States shows that fluctuations of nearly 2 per cent, occur in its composition, as estimated by the nitrogen present ; and accounts thereby for the variations com plained of in its heating power.
Many geological problems may be solved by a consideration of the effect of slight thermal changes. Herr Herzfeld gives the amounts of water required to dissolve one part of Ca at different centigrade temperatures as follows : —
15° 20° 26° 30° 36° 40° 46° 50° 55° 60° 66° 70° 75° 80° 776 813 848 885 924 962 1004 1044 1108 1158 1244 1330 1410 1484
It appears from this that cooling water has a progressive capacity for dissolving lime, whilst a saturated solution at any ordinary temperature must throw out that substance on any degree of heating.
In addition, M. Cabot shows that a solution of sodium chloride dis- solves more lime at all temperatures and concentrations than a corre- sponding solution of potassium chloride ; that in all cases the maximum solubility of lime in the chloride solution occurs when the temperature is lowest; and that in solutions of all concentrations the solubility decreases regularly as the temperature increases.
Thus may be explained what 8ir John Murray, at the last meeting of the British Association, called " the puzzling rdle " played in all deep- sea deposits by carbonate of lime, which varies in abundance according to the depth of the ocean and the temperature of the surface waters. Such deposits would increase at temperatures warmer than their place of origin, but would tend to disappear altogether in colder depths.
This exceptional condition of solvency does not extend to the case of silica, which follows the rule of being more soluble in warmer water ; and the curious alternations of chalk and flint, of limestone and chert, of
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