22 FRANK D. ADAMS 



These major breaks would seem to be as well marked and as impor- 

 tant as those which characterize the separation of the Eo-Paleozoic 

 and the Neo-Paleozoic in eastern America, or perhaps as that which 

 brings to a close the Paleozoic succession in Europe. 



If, as our knowledge of the pre-Cambrian becomes more complete, 

 the correlation of these rocks over great areas by a time relation to 

 diastrophic epochs proves to be generally applicable, we have a basis 

 of correlation of great value and importance. This will constitute 

 a great advance as compared with our present methods, which afford 

 no adequate means of determining the relative values of unconformi- 

 ties and thus the successions in the most distant parts of the world 

 are now being matched with each other and an unwarranted satis- 

 faction is manifested if the number of unconformities in the pre-Cam- 

 brian succession in different continents is approximately identical, 

 and a sure and certain hope that all will prove to be satisfactory is 

 expressed if there is no agreement. 



All that we really know at present is that 

 there are great sequences of pre-Cambrian sedimentary formations, separated 

 by many gaps from each other, which give one picture, growing less distinct in 

 outline the farther back one goes, of the remotest periods of geological history, 

 or, in other words, of periods of the earth's pre-historic age which is, according 

 to the author's opinion, probably of greater length than all subsequent geological 

 time.' 



It is beheved, however, that through the recognition of these diastro- 

 phic epochs, the dominant outlines of these pictures may perhaps 

 be more clearly brought out and the relative values of the different 

 parts thrown into relief in the case of each individual positive element, 

 and that these epochs which have marked the successive stages of 

 advance in Paleozoic and Mesozoic times, may thus be employed 

 with advantage in deciphering the history of the pre-Cambrian as 

 well. 



DISCUSSION 



CHARLES R. VAN HISE 



It is with pleasure that I discuss briefly Dr. Adams' paper, since, allowing 

 for differences of terminology, I find him in nearly complete accord with the 



I J. J. Sederholm, Explanatory Notes to Accompany a Geological Sketch Map of 

 Fenno-Scandinavia, Helsingfors, 1908, p. 31. 



