COMMENTS ON THE THEORY' OF IMBOROVE 1.) 



SCHEMATIZATION IN OEOLO(;i(: WRl IING 



To those who still want to see something catastrophic in a regular 

 beating of a pulse of the earth, I might be allowed to point out once 

 more that the period of this terrestrial pulse excludes all ( omparison 

 with catastrophes in a human sense. One pulse-beat of the earth, in 

 the sense as described by Umbgrove, takes about 250 million years. 

 So what is a day or a year or even man's life span in comparison 

 to one beat of the pulse of our earth? 



Not every geologist adheres to Professor Umbgrove's picture of a 

 strict synchronization of many different processes in the earth to a 

 pulse beat of 250 million years. Of course, extrapolation from the 

 present is so large that many differences of opinion may arise. 

 However, apart from doubts about the strictness of synchronization 

 and the exact length of the individual periods in earlier parts of the 

 earth's history, time spans of 250 million years, more or less, are 

 quite well established for many different sorts of variations in in- 

 tensity of geological phenomena. Umbgrove's theorv' of many differ- 

 ent terrestrial processes, regularly varying together with such extreme 

 slowness will, on the other hand, most forcibly instil into a non- 

 geologist this distinction between human history and that of the earth. 



Of course, one cannot all the time stress the importance of these 

 immense time-spans in geological writing, and it is here that many 

 geologists perhaps too freely express what their imagination sees 

 when looking at the slow history of the earth through eyes expressly 

 trained to speed up this development one million times. Every 

 amateur who has taken slow-motion pictures will know what a factor 

 of one million in speed-up implies. 



To illustrate this, I will take just one example from geologic 

 literature: the process of mountain building or orogeny. The creation 

 of our present major mountain chains, such as the Alps, the Hima- 

 layas and the Andes, has taken some 50 million years. Earth move- 

 ments over that period were of the 1 nun a year type. Before that 

 time the earth's crust was much more quiet, and mov'ements of the 

 order of 1 mm per century were normal. Moreover, this earlier, more 

 stable period was of much longer duration. It lasted something 

 between 100 million or 200 million vears. 



We geologists now are apt to speak, in our speeded-up version of 

 the history of the earth, of a 'catastrophic period of mountain build- 



