THE DEVELOPMENT OF REASONING. 65 



ceeded to generalization, and then rose or is rising to unification in fami- 

 lies or genetic groups. In the days of Aristotle the method of classi- 

 fication was successive division by difference, then under the influence 

 of Bacon and Linnaeus the method became one of successive grouping 

 by resemblance, while Darwin and his successors introduced the method 

 of classifying by genetic relation or consanguinity ; and during our own 

 generation descri[)tive science has given way largely to systemic science, 

 and thereb}' species and genera are increasing less rapidly in number 

 than in fullness of meaning. 



The several stages in development of the modes of acquiring knowledge 

 are none the less real in that they overlap and blend in the development 

 of the branch of science, in the intellectual expansion of the individual; 

 and the}' are none the less veritable that the empiric stage grades into 

 the scientific stage so imperceptibly that no sharp line may be drawn 

 between ; for such is the law of becoming, by which all things in tlie 

 universe are made. 



Growth of Knowledge of the Earthcrust. 

 the stage of speculation. 



In geology, as in other branches of knowledge, the four methods of 

 acquisition — observation, discrimination, generalization and genetic clas- 

 sification — have been employed in normal order. At first the individual 

 geologist, enriched by heritage of observing faculty and reasoning power 

 developed through generations, began to see more in the rocks than his 

 ancestors were able to perceive, and quickly i)assed into the first stage of 

 reasoning. Differences in color, form and size were detected, and dis- 

 crimination progressed and grew into speculation, and the ratio of 

 liypothesis to observed fact grew large, as is ever the case among laymen 

 and the illiterate. During this stage attention was commonly attracted 

 and held only by the rare or remote, and the facts near at hand were 

 ignored even if they were i)erceived, and so the [)rimitive geologist found 

 matter of interest chiefly in deep mines and distant mountains, and was 

 blind to the normal strata ])eneath his feet, to the residua forming the 

 soil on which he lived, to the alluvial and glacial deposits in which the 

 later history of the earth is recorded. Throughout this stage the body 

 of observed fact was meager, while " theories of the earth " abounded, 

 though few were so tangil)le as to l)e preserved in definite form. 



Such was the stage of reasoning from the unlike in the development of 

 geology, yet it was the necessary precursor of a higher stage, and has its 

 parallel in each branch of knowledge. The processes of thought were 



