February 18, 1910] 



SCIENCE 



255 



tends ever to vibrate in harmony. What- 

 ever disturbs the equilibrium of any part, 

 affects the whole. Diastrophism initiates 

 change. The sun's energy modifies the re- 

 sulting surface features, and physical, 

 chemical and biotic reactions carry the ef- 

 fects into all the phenomena of nature. 

 Were nature unchanging, time would pass 

 unrecorded. It is through the sequence of 

 unlike effects that we may establish a 

 chronology, and that sequence begins with 

 diastrophism as the initial cause and ends 

 with evolution as the final effect. 



DIASTROPHISM THE BASIS OP CORKELATION 



It follows logically from the preceding 

 that the initial cause of change, diastro- 

 phism, is necessarily the ultimate basis of 

 all correlation. Chamberlin^^ has very re- 

 cently put this conclusion strongly and 

 clearly. 



On a preceding page the law of perio- 

 dicity of diastrophism is stated as deduced 

 from the observed occurrences of dias- 

 trophic movements in different dynamic 

 provinces. According to that law it is in- 

 activity, rather than activity, of earth 

 movements, which has contemporaneously 

 characterized the whole earth. That is to 

 say, the normal condition of the stresses 

 and resistances in the earth's crust is a 

 close approach to equilibrium, and dis- 

 turbances of that equilibrium have in gen- 

 eral been manifested at the surface by 

 slight movements only. More emphatic 

 movements have been relatively occasional 

 and provincial (circum-oceanic), and Ave 

 may add that they have been more re- 

 stricted and less prolonged as they have 

 been more vigorous. 



This law governs the relation of dias- 

 trophism to correlation. 



The long eras of inactivity, the base- 



" Chamberlin, T. C, " Diastrophism the Ulti- 

 mate Basis of Correlaiion," Jour, of Geol. 



level eras for the whole world, have been 

 essentially contemporaneous, though not 

 conterminous or even approximately con- 

 terminous. But their very great duration, 

 from which their essential contemporane- 

 ity results, unfits these eras for any except 

 the broadest outline of classification, so far 

 as they themselves are concerned. Yet the 

 topographic, climatic and environmental 

 uniformity which developed during these 

 eras of inactivity affords the best condi- 

 tions for correlation by other criteria. 

 Thus the base-level eras are to the history 

 of paleogeography what the broad and 

 deep foundations of a great building are to 

 the many rooms of the superstructure. 



Thus for inactivity. The periods of ac- 

 tivity present different phenomena, differ- 

 ently distributed in place and time. We 

 may define a period of activity as com- 

 prising that time which is marked initially 

 by decided continental movements and cul- 

 minates in notable erogenic uplifts. Penn- 

 sylvanian and Permian constituted such a 

 period about the North Atlantic, as witness 

 the development of lands, mountains and 

 sediments in western Europe and eastern 

 North America. The recognized active 

 periods appear to characterize distinct 

 dynamic provinces which are ocean basins, 

 as already described. Thus with regard 

 to their value in correlation we may say: 

 Periods of active diastrophic movement 

 have ieen shorter than eras of iase-level- 

 ing, and consequently define time divisions, 

 which are more nearly commensurate with 

 those of current geologic standards. They 

 are, however, still long, and their value is 

 in broad fundamental classification. 



Diastrophic activity is, moreover, con- 

 temporaneously manifested only in and 

 around the dynamic province in which it 

 originates. During any particular period 

 it has been peculiar to a particular oceanic 

 basin or group of basins and has disturbed 



