890 



SCIENCE. 



[N. S. Vol. IX. No. 235. 



limitations of time. But in the earlier part 

 of the century geological attention was ab- 

 sorbed in the great phenomena that testify to 

 the vastness of the earth's history. The time 

 for the study of limitations had not come. 



Nevertheless, however inevitab le must 

 have been the ultimate recognition of limi- 

 tations, it remains to be frankly and grate- 

 fully acknowledged that the contributions 

 of Lord Kelvin, based on physical data, 

 have been most powerful influences in has- 

 tening and guiding the reaction against the 

 extravagant time-postulates of some of the 

 earlier geologists. With little doubt, these 

 contributions have been the most potent 

 agency of the last three decades in restrain- 

 ing reckless drafts on the bank of time. 

 Geology owes immeasurable obligation to 

 this eminent physicist for the deep interest 

 he has taken in its problems and for the 

 profound impulse which his masterly com- 

 putations and his trenchant criticisms have 

 given to broader and sounder m.odes of 

 inquiry. 



At the same time, it must be recognized 

 that any one line of reasoning, however 

 logically and rigorously followed, is quite 

 sure to lead astray if it starts from limited 

 and uncertain premises. It is an easy 

 error to press the implications of any single 

 phase of the complex phenomena of geology 

 until they shall become scarcely less mis- 

 leading than the looser speculations which 

 they seek to replace. A physical deduction 

 which postulates an excessively short geo- 

 logical history may as easily lead to false 

 views as did the reckless license of earlier 

 times. Interpretations of geological and 

 biological phenomena made under the 

 duress of physical deductions, unless the 

 duress be certainly known to be imperative, 

 may delay the final attainment of the real 

 truth scarcely less eifectually than interpre- 

 tations made on independent grounds in 

 complete negligence of the testimony of 

 physics. It is in the last degree important 



that physical deductions and speculations 

 should be regarded as positive limitations 

 only so far as thej' are strictlj' demonstra- 

 tive. Falling short of demonstration, they 

 are worthy to be regarded as moral limita- 

 tions only so far as they approach moral 

 certainty. In so far as they are drawn 

 from doubtful assumptions, they are as ob- 

 viously to be placed in the common cate- 

 gory of speculations as are those tentative 

 conceptions which are confessedly but the 

 possible foreshadowings of truth. The fas- 

 cinating impressiveness of rigorous mathe- 

 matical analysis, with its atmosphere of 

 precision and elegance, should not blind us 

 to the defects of the premises that condition 

 the whole process. There is, perhaps, no 

 beguilement more insidious and dangerous 

 than an elaborate and elegant mathemat- 

 ical process built upon unfortified premises. 

 Lord Kelvin's address is permeated with 

 an air of retrospective triumph and a tone 

 of prophetic assurance. The former is 

 fairly warranted to the extent that his at- 

 tack was directed against the ultra wing of 

 the uniformitarian school of the earlier 

 decades. It might be wholesome, however, 

 to remember that there were other camps 

 in Israel even then. There were ultra- 

 conservatives in chronology as well as 

 ultra-radicals. There were ultra-catastro- 

 phists as well as ultra-uniformitarians. 

 Lord Kelvin's contributions have as sig- 

 nally failed to sustain the former as they 

 have signally succeeded in overthrowing the 

 latter. The great body of serious geol- 

 ogists have moved forward neither by the 

 right flank nor by the left, but on median 

 lines. These lines have lain, I think, 

 rather in the field of a qualified uniformi- 

 tarianism than in the field of catastrophism. 

 Even the doctrine of special acceleration in 

 early times, or at other times, has made 

 only qualified progress toward universal 

 acceptance. The body of competent geol- 

 ogists to-day are probably more nearly dis- 



