THE 
GEOLOGICAL MAGAZINE. 
NEW SERIES. DECADE II. VOL. IV. 
No. I.— JANÜARY, 1877. 
OK.IC3-HsTA.Xi AETICLES. 
I. — On Evolution in Geology. 
By "W. J. Sollas, B.A., F.G.S., 
Lecturer on Geology, Cambridge University Extension. 
HAT tbe energy of the earth and the sun is a continually diminish- 
ing quantity, and must at the beginning of geologic bistory 
have been far in excess of its present amount, are propositions tbat 
few at tbe present day would be found to deny ; but tbe exact influence 
of this greater quantity of energy on geologic changes bas not, I 
believe, been hitberto fully discussed. 1 
The Sun . — Tbe Sun is a large and exceedingly hot star, cooling 
slowly in space, and it is because it is so large and bot tbat it bas 
been able to supply our world and all tbe other members of its 
System witb so much beat for so long a time. It is daily losing 
beat, and it is tbe beat thus lost by tbe sun, and gained in part by 
us, tbat supplies the energy requisite for tbe work of most denuding 
agents. 
If tbe sun tben be a cooling body, its störe of energy must have 
been greater yesterday than it is to-day, by exactly tbe equivalent 
of tbe amount of beat it bas radiated since tben ; and so of all 
previous yesterdays : so tbat if we go back far enough in time, we 
sball reacb a period when the störe of energy in tbe sun was too 
great to permit of its existence in its present state. Tbis period, as 
calculated by Sir William Thomson, is placed as far back as from 
100 to 500 millions of years ago. 2 But it is a law of cooling bodies 
that tbey cool tbe quicker tbe higher tbeir temperature is above tbat 
of tbe surrounding medium. The space in wbicb all worlds exist, 
the medium wbicb surrounds our sun, appears to have no sensible 
1 The views contained in this paper, the sources of some of which will be obvious, 
were first expressed hefore the Halifax Philosophical Society, in a lecture which I 
delivered in 1874, and afterwards in a paper read before the Leeds Geologists’ 
Association. They are now printed in a Condensed form and rather as suggestions 
than anything eise. 
2 The increased amount of energy in the sun does not imply a corresponding 
elevation of temperature ; to a great extent such additional energy was poten- 
tial, but from all we know it seems most probable that an increase in potential 
would be aecompanied in this case by an increase in kinetic energy, and so we may 
safely assume that the temperature of the sun rises in an ascending curve as we 
proceed backwards in time. The more rapid conversion of potential into kinetic 
energy, which probably occurred at intervals, would produce fluctuations in 
temperature, and so the temperature curve in the sun’s bistory is probably not a 
simple line, but varied by numerous minor undulations. 
DECADE II. — TOL. IV. — NO. I. 1 
