224 THE AGE OF THE EAKTH AS AN ABODE FITTED FOR LIFE. 



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 computations and 

 his trenchant criticisms have given to broader and sounder modes of 



inquiry. 



At the same time it uuist be recognized that any one line of reason- 

 ing, 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 mislead- 

 ing than the looser speculations which they seek to replace. A physi- 

 cal deduction which postulates an excessively short geological 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 phj^sical deductions, unless the duress be certainly 

 known to be imperative, may delay the final attainment of the real 

 truth scarcely less effectually than interpretations 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 they are 

 strictly demonstrative. Falling short of demonstration, they are 

 worthy to be regarded as moral limitations only so far as they 

 approach moral certainty. In so far as they are drawn from doubtful 

 assumptions, they are as obviously to be placed in the common cate- 

 gory of speculations as are those tentative conceptions which are con- 

 fessedly but the possible foreshadowings of truth. The fascinating 

 impressiveness of rigorous mathematical analyses, 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 mathematical process built upon unfortified premises. 



Lord Kelvin's address is permeated with an air of retrospective 

 truimph and a tone of prophetic assurance. The former is fairly war- 

 ranted to the extent that his attack Tvas directed against the ultra wing 

 of the unif ormitarian school of the earlier decades. It might be whole- 

 some, 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-catastrophists as well as ultra-uni- 

 formitarians. Lord Kelvin's contributions have as signally failed to 

 sustain the former as they have signally succeeded in overthrowing 

 the latter. The great body of serious geologists have moved forward 

 neither by the right tiank 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 



