124 GEOLOGICAL CHANGE, AND TIME. 



ceptions of the high antiquity of the globe. Some six thousand years 

 liad previously been believed to comprise the whole life of the j^lanet, 

 and indeed of the entire universe. When the curtain was then tirst 

 raised that had veiled the history of the earth, and men, looking beyond 

 the brief span within which they had supposed that history to have 

 been transacted, beheld the records of a long vista of ages stretching 

 fiir away into a dim illimitable past, tlie prospect vividly impressed 

 their imagination. Astronomy had made known the immeasurable 

 fields of space; the new science of geology seemed now to reveal bound- 

 less distances of time. The more the terrestrial chronicles were studied 

 the farther could the eye range into an antiquity so vast as to dety all 

 attempts to measure or define it. The progress of research continually 

 furnished additional evidence of the enormous duration of the ages 

 that preceded the coming of man, while, as knowledge increased, periods 

 that were thought to have followed each other consecutively were found 

 to have been separated by prolonged intervals of time. Thus the idea 

 arose and gained universal acceptance that, just as no boundary could be 

 set to the astronomer in his free range through space, so the Avhole of by- 

 gone eternity lay open to the re(i[uirements of the geologist. Playfair, 

 re-echoing and expanding Hutton's language, had declared that neither 

 among the records of the earth, nor in the planetary motions, can any 

 trace be discovered of the beginning or of the end of the present order 

 of things; that no symptom of infancy or of old age has been allowed 

 to appear outhe face of nature, nor any sign by which either the past 

 or the future duration of the universe can be estimated; and that 

 although the Creator may put an end, as he no doul)t gave a begin- 

 ning, to the present system, such a catastrophe will not be brought 

 about by any of the laws now existing, and is not indicated by anything 

 which we i)er(;eive. This doctrine was naturally espoused with warmth 

 by the extreme uniformitarian school, which required an unlimited 

 duration of time for the accomplishment of such slow and quiet cycles 

 of change as they conceived to be alone recogniza])le in the records of 

 the earth's past histoiy. 



It was Lord Kelvin, who, in the writings to which I have already 

 referred, first called attention to tlie fundamentally erroneous nature 

 of these conceptions. He pointed out thar from the high internal tem- 

 perature of our globe, increasing inwards as it does, and from the rate 

 of loss of its heat, a limit may be fixed to the planet's antiquity. He 

 showed that so far from there being no sign of a beginning, and no 

 prospect of an end, to the present economy, every lineament of the 

 solar system bears witness to a gradual dissipation of energy from some 

 definite starting point. No very precise data were then, or indeed are 

 now, available for computing the interval which has elapsed since that 

 remote commencernent, but he estimated that the surface <^)f the globe 

 could not have c(msolidated less than twenty millions of years ago, for 

 the rate of increase of temi)erature inwards would in that case have 



