August 29, 1902.] 



SCIENCE. 



325 



themselves professional geologists, are 

 teachers of geology in academies and col- 

 leges, or are even members of the staff 

 of state or government surveys. These men 

 have gone further than the local geologist; 

 but perhaps they have been led into the 

 subject for somewhat the same reason, by 

 its easy start as an observational science. 

 A man may begin his career as a geologist 

 by making a few observations here and 

 there and giving a guess as to their mean- 

 ing. With this beginning he becomes more 

 and more interested, until finally he decides 

 to make geology his profession. 



In some cases following this decision the 

 necessity is seen for obtaining a working 

 knowledge of the basal sciences. But too 

 often men who have entered upon geo- 

 logical work have received no adequate 

 training in chemistry, in physics, in 

 biology ; and therefore at the outset wholly 

 lack the tools to successfully interpret the 

 phenomena which they observe. But such 

 inadequately trained men feel that a satis- 

 factory explanation of any phenomenon 

 must involve a statement of the underlying 

 chemical or physical or biological princi- 

 ples. In such cases it is safe to say that the 

 explanations given are extremely partial, in- 

 cluding only a modicum of truth, and more 

 often than not are absolutely fallacious. 

 Indeed, no other result can be expected 

 from one who lacks a" working knowledge 

 of the principles of physics, chemistry and 

 biology. Occasionally there is a clear- 

 sighted, capable man, lacking in adequate 

 training, who does important geological 

 work simply because he knows his limita- 

 tions, and there stops. But this is very 

 exceptional indeed ; and the physical ex- 

 planations offered by many for various 

 geological phenomena are no less than 

 grotesque. 



It has been made plain that a working 

 knowledge of the sciences basal to geology 

 is necessary in order to advance its prin- 



ciples. But I go even further, and hold 

 that such basal knowledge is absolutely 

 necessary in order to do even the best de- 

 scriptive work. Suppose a man to be stand- 

 ing before some complex geological phe- 

 nomenon. The whole intricate interlocking 

 story is engraved upon the retina of his eye 

 with more than photographic accuracy. The 

 image on the retina is absolutely the same 

 in the eye of this experienced geologist and 

 that of a child. Yet if the child be asked 

 to state what he sees, his statements will 

 be of the most general kind and may be 

 largely erroneous. The experienced geol- 

 ogist with a knowledge of the principles 

 of physics and chemistry and biology in- 

 terprets the phenomena imaged in terms of 

 these subjects. The engraving on his retina 

 is the same as that of the child, but his 

 brain perceives the special parts of the 

 picture of interest to him in their true pro- 

 portions. He understands what is im- 

 portant, what is unimportant ; he must 

 select and record the things which are im- 

 portant. If he attempted to record all that 

 is imaged in his eye, a notebook would be 

 filled with the phenomena to be described 

 at a single exposure ; and yet half the story 

 would not be told. Good descriptive work 

 is discriminative. Good descriptive work 

 picks out certain of the facts as of great 

 value ; others of subordinate value ; and 

 others of no value for the purposes under 

 consideration. How then can this discrim- 

 ination be made? How can the facts be 

 selected which are of service? Only by 

 an insight into the causes which may have 

 produced the phenomena. Without this 

 insight to some extent at least a description 

 is absolutely valueless. So far as the geolo- 

 gist has such insight, his description is 

 valuable. 



It is frequently urged in opposition to 

 the above that, 'If a person has theories in 

 reference to the phenomena which he 

 observes his descriptions will be erroneous ; 



