Bar veil — Growth of Knowledge of Earth Structure. 135 



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- 

 ing the slow settling of opinion may be cited in regard to 

 the significance of the dip of the Trias sic formations of 

 the eastern United States. The strata of the Massachu- 

 setts-Connecticut basin possess a monoclinal easterly dip 

 which averages about 20 degrees to the east. Those of 

 the New Jersey-Pennsylvania- Virginia basin possess a 

 similar dip to the northwest. Both basins are cut by 

 great faults and the dip is now accepted by practically 

 all geologists as due to rotation of the crust blocks 

 away from a geanticlinal axis between the two basins. 

 Jiidward Hitchcock, whose work from the first shows an 

 interpretative quality in advance of his time, states in 

 1823 (6, 74) regarding the dip of the Connecticut valley 

 rocks : 



