KNOWLEDGE OF EARTH STRUCTURE 155 



The Prolonged Influence of Outgrown Ideas. 



Those interested in any branch of science should, as a 

 matter of education, read the history of that special sub- 

 ject. A knowledge of the stages by which the present 

 development has been attained is essential to give a 

 proper perspective to the literature of each period. 

 Much of the existing terminology is an inheritance from 

 the first attempts at nomenclature, or may rest upon 

 theories long discarded. Popular notions at variance 

 with advanced teaching are often the forgotten inherit- 

 ance of a past generation. 



Gneiss, trap, and Old Red Sandstone are names which 

 we owe to Werner. The "Tertiary period " and "drift" 

 are relics of an early terminology. The geology of 

 tourist circulars still speaks of canyons as made by "con- 

 vulsions of nature. " Popular writers still attribute to 

 geologists a belief in a molten earth covered by a thin 

 crust. Within the present century the eighteenth cen- 

 tury speculations of Werner and his predecessors, postu- 

 lating a supposed capacity of water to seep through the 

 crust into the interior of the earth, resulting in a hypo- 

 thetical progressive desiccation of the surface, views long 

 abandoned by most modern geologists, have been revived 

 by an astronomer into a theory of " planetology. " 



A review of the literature of a century brings to light 

 certain tendencies in the growth of science. Each decade 

 has witnessed a larger accumulation of observed facts 

 and a fuller classification of these fundamental data, but 

 the pendulum of interpretative theory swings away from 

 the path of progress, now to one side, now to the other, 

 testing out the proper direction. For decades the under- 

 standing of certain classes of facts may be actually retro- 

 gressive. A retrospect shows that certain minds, keen 

 and unfettered by a prevailing theory, have in some 

 directions been in advance of their generation. But the 

 judgment of the times had not sufficient basis in knowl- 

 edge for the separation and acceptance of their truer 

 views from the contemporaneous tangle of false inter- 

 pretations. 



An interesting illustration of these statements regard- 



