72 THE JOURNAL OF GEOLOGY. 



are therefore repeatedly introduced with others in the systematic 

 advance of the course ; and the student may gauge his progress 

 by the increased meaning that these illustrations gain on every 

 return. 



Let us next consider the development of a deductive geo- 

 graphical scheme, by which external observation is to be supple- 

 mented and completed. Let it be understood at the outset that 

 to exceed the variety of nature is an extended enterprise, a 

 remote and ideal goal, towards which we strive. Let no exces- 

 sive flight of theory carry us far from the earth and overcome us 

 in mid-air. Let us carefully guard against an unwarranted wan- 

 dering of the imagination by frequent conferences with the facts 

 of observation, hoping to return, like old Antseus, strengthened 

 for new efforts after every touch of Mother Earth. 



Tlie deductive geographical sclieme. — It is the fundamental 

 generalization of elementary geology to note that the lands are 

 wasting away under the destructive attack of the weather. The 

 hardest rocks decay ; their waste creeps and washes down to 

 lower and lower levels, never satisfied till it reaches the sea. 

 However broad a plateau, however lofty a mountain range, it 

 must, if time enough be allowed, be worn down to sea level 

 under the weather ; and the unceasing beat of the sea on its 

 shores must reduce it still lower to a submarine platform. Since 

 the remote beginning of geological time there has been time 

 enough and plenty to spare to reduce all the lands to such a 

 submarine platform ; but as high lands still exist, it must be con- 

 cluded that they are revived from time to time and from place 

 to place by some forces antagonistic to those of subaerial denu- 

 dation. In whatever way a new mass is offered to the wasting 

 forces, let us call the forces that uplift it constructional forces ; 

 and the forms thus given, constructional forms. Let all the 

 forces of wasting be called destructional forces; let the sea level 

 surface, down to which a sufficiently long attack of the destruc- 

 tional forces will reduce any constructional form, be called the 

 ultimate baselevel ; and let the portion of geological time 

 required for the accomplishment of this task be called a geo- 



