ISOSTASY AS A RESULT OF EARTH SHRINKAGE 215 



of the entire system. Since some fairly recent mountains show- 

 evidence of several deformations we would perhaps not be wrong 

 in concluding that mountain ranges which originated far in the 

 past have been frequently rejuvenated. The records of times of 

 such rejuvenations are rarely found. Added to those ranges 

 which took up the shortening of the crust on the continents there 

 were probably many ranges on the sea bottom which could have 

 left no time record. Therefore, for these reasons, if we consider 

 that the upper rectangle in Figure 4 represents continuous diastro- 

 phism, it is likely that incomplete geological records would show 

 something of the order of the lower diagram (Fig. 4). 



If we consider that individual orogenic disturbances on the 

 average continue from one-third to one-half of a period, then the 



Fig. 4. — Diagrams illustrating the replacing of a complete series of deformations 

 (above) by a fragmentary series of records (below) because of incomplete geological 

 data. 



records of the times of deformation, which have been compiled, 

 are surprising, not in that they show infrequent deformations, but 

 that they show an almost uninterrupted series of orogenic move- 

 ments in one part of the world or another. They scarcely illustrate 

 a contemporaneous origin of two large mountain systems. The 

 most complete records, which are of the Cenozoic disturbances, 

 show an almost equal distribution of diastrophism in the different 

 divisions of the era. Only where the records have been much 

 effaced farther back in the time scale are there indications which 

 point toward periodicity. Even in the Paleozoic, diastrophic 

 movements do not appear to come especially at the end of periods. 

 In an article compiled by R. T. Chamberlin,^ the times of Paleozoic 

 deformation are given. A critical examination of the evidence of 



' R. T. Chamberlin, Jour, of GeoL, Vol. XXII (1914), p. 315. 



