﻿TV. J. SoUas — On Evohition in Geology. 5 



surface ; the difference in temperature might not be very great, but 

 it would exist. From the increased rainfall would necessarily follow 

 a more rapid corrosion of the general surface of the land, and a 

 speedier degradation of its general level. The sculpturing of hills 

 and valleys and the delivery of detritus to the sea must have pro- 

 ceeded at a swifter rate ; and indeed all the activities of rain and 

 rivers would be stimulated to relatively greater energy. 



3. Subterranean Waters. — Not only would the amount of these be 

 augmented by the increased rainfall, but they would be influenced 

 by the higher temperature of the earth's crust ; thus in the present 

 period percolating water must descend on the average 51 feet below 

 the zone of constant temperature in order to rise 1° in temperature ; 

 4,000 years after the permanent incrustation of the earth, the same 

 descent would be accompanied by an elevation of 5° in temperature. 



4. Marine Denudation. The Waves. — The difference of tempera- 

 ture which produces the rainfall also drives the winds in their 

 courses, just as truly as the difference in temperature between the 

 boiler of a steam engine and the external air drives the piston. 

 Augment the difference and the winds will flow faster and more 

 violently, just as certainly as fresh fuel will urge the engine with 

 greater activity. Thus the denudation accomplished by the winds 

 will also be accelerated, especially that disintegration of sea-clifts 

 which they produce indirectly. For it is the winds ruflSing the ocean 

 which produce the sea- waves, and it is the energy of these directed 

 to the battering down of the cliffs along every coast-line which pro- 

 duces a great part of the work of marine denudation. 



Tides. — These are due to the rotation of the earth between the 

 attracting bodies of the sun and moon, and since this rotation must 

 have been more rapid the further back we recede in time, so must it 

 have conferred greater energy on the actions of the tides. Let the 

 velocity of the earth's rotation be doubled, and the tides will rise 

 four times instead of twice in every twenty-four hours, and with 

 greater frequency will attain also greater velocity. But it is the 

 tides and tidal currents which are, amongst others, the most per- 

 sistent agents in coast-line transportation ; and thus the detritus 

 produced with increased rapidity by the disintegrating actions of 

 the rain and waves, will be with corresponding rapidity carried 

 away to preserve the coast-line constantly exposed to renewed decay. 



Marine Currents. — All these, excepting those produced by the 

 tides, are ultimately due to differences in temperature on which 

 the winds also depend, and thus will likewise flow with accelerated 

 velocity, and consequently their influence as transporting agents 

 will be correspondingly exalted. 



Deposition. — The rate of deposition is always directly proportional 

 to the rate of denudation, and may be said at any particular time to 

 equal it. Thus any increase in the rate of denudation will be 

 necessarily accompanied by a corresponding increase in the deposi- 

 tion of sediment. If we look for any direct proof of this, there is 

 but little to be found. Prof. Phillips has shown that the proportion 

 of the number of fossil species to the thickness of its strata con- 



