BASIS OF PRE-CAMBRIAN CORRELATION 2$ 



Dr. Adams in his paper repeats the quotation from Willis and makes an 

 identical suggestion as to correlation, but implies that this is done upon the basis 

 of diastrophism. Evidently he thinks that there is an "unwarranted satisfac- 

 tion" in the first case and not in the second. 



Each unconformity between any two series of the Canadian region or of 

 China means that between their depositions there has been an epoch of dias- 

 trophism and one of erosion. I should be interested to know how the extents 

 and the magnitudes of pre-Cambrian diastrophisms are to be determined except 

 by studying the extents and magnitudes of the unconformities, that is, the extent 

 and amount of the foldings, metamorphisms, erosions, etc., which intervened 

 between the various series. In the paper which I have just read I pointed out 

 that some unconformities are local, some regional, and some probably inter- 

 continental. Adams points out that diastrophism may be regional or intercon- 

 tinental. Is the distinction between the two greater than chfference in language ? 

 One we may suggest talks English, the other Esperanto. Evidently if satis- 

 faction is unwarranted in one case it is unwarranted in the other. 



I am obliged to dissent altogether from the reasoning in Dr. Adams' paper 

 which makes discriminations as to the magnitudes of the various breaks, upon 

 the basis of Willis' hypothesis of positive and negative continental elements, and 

 upon assumptions as to the sources of the thrusts. Even if these theories be 

 assumed to be correct we do not know that they apply to the North American 

 pre-Cambrian region, for we know nothing of the extent and distribution of the 

 various pre-Cambrian series which are hidden under later rocks. In the western 

 United States where extensive areas of pre-Cambrian protrude through the later 

 rocks, and also in the Mississippi Valley, where are isolated areas of pre-Cambrian, 

 several pre-Cambrian series occur, some of which are probably the equivalent of 

 the series found in the Lake Superior region. Evidently the various pre-Cam- 

 brian diastrophic movements cannot be assumed to be limited to the surface areas 

 of pre-Cambrian. 



The question of the major groupings of the pre-Cambrian series I shall not 

 attempt to go into in detail, since to do this would result in leaving less emphatic 

 the reality of the accord as to the pre-Cambrian succession which has now come 

 about and which I trust has come to stay between the Canadian and United 

 States geologists, through the acceptance for Canada of the succession mainly 

 worked out in a great area along the southern border of the pre-Cambrian 

 region. 



However, I may recall that I fully discussed the major classification of the 

 pre-Cambrian in my presidential address before the Geological Society a year 

 ago, and gave reasons for the primary divisions of the pre-Cambrian into the 

 Archean and Algonkian. In that address I gave objections to a zoic classifica- 

 tion, similar to but not identical with that which Dr. Adams adheres to. His 

 proposed major classification is eo-proterozoic, meso-proterozoic, and neo- 

 proterozoic. These terms imply that the pre-Cambrian had three distinctive 

 life periods, an eo, a meso, and a neo. This may be the case, but until fossils. are 



