A CENTURY OF GEOLOGY. 27 1 



of geologic histoiy sea and land frequently and comploteh' changed 

 places. Abundant evidence of this was supposed to be found in the 

 unconformities so frequent in the stratified series. The tendency of 

 that time was toward a belief in up-and-down mov^ements, back-and- 

 forth changes, without discoverable law rather than progressive 

 onward movement. On first thought it might seem that such lawless 

 movement was rather in keeping with catastrophism than uniformita- 

 rianism. But not so, for the movements are supposed to be verv slow. 

 Again, it might seem on first thought that gradual progressive change — 

 in a word, evolution — would l)e peculiarly in accord with uniformita- 

 rian ideas. But again not so, because this doctrine was, above all, a 

 revulsion from the idea of supernatural purpose or design or goal con- 

 tained in catastrophism. Uniformitarianism strongly inclined toward 

 purposelessness, because of , its supposed identity with naturalism. 

 Thus for a long time, and still with man}" geologists, the tendency is 

 toward a belief in irregular movements without discoverable law — 

 toward instability of even the greatest features of the earth, viz, sea 

 basins and continental arches. Geology for them is a chronicle, not a 

 life histor3\ 



The contrary movement of thought ma}" be said to have commenced 

 with Dana. Dana studied the earth as a unit, as in some sense an 

 organism developing by forces within itself. The history of the earth 

 is a life history moving progressively toward its completion. The 

 forces originating oceanic basins and continental arches still continue 

 to deepen the former and enlarge the latter. From this point of 

 view oceanic basins and continental arches must have always been 

 substantially in the same places. Oscillations there have been at all 

 times and at all places, but they affect mainly the outlines of these 

 great features, though sometimes atiecting also the interior of conti- 

 nents and mid-sea bottoms, but not sufficiently to change greatly their 

 general form, much less to interchange their places. 



Such is the doctrine of permanency of oceanic basins. It is undoubt 

 edly a true doctrine, but must not be held in the rigid form character- 

 istic of early thought. The forces originating oceanic basins still con- 

 tinue to deepen them and to increase the size and height of contuients, 

 but other forces are at work, some antagonizing (i. e., cutting down 

 the continents and filling up the ocean beds), and still others determined 

 by causes we little understand, by oscillations over wide areas, greatly 

 modifying and often obscuring the efiects of the basin-making move- 

 ments. Here, then, we have two kinds of crust movements: The one 

 fundamental and original, determining the greatest features of the 

 earth and moving steadily onward in the same direction, ever increas- 

 ing the features which it originates; the other apparently lawless, uncer- 

 tain, oscillating over very wide areas, modifying and often obscuring 

 the effects of the former. The old uniformitarians saw only the efiects 

 SM lyuu 2u 



