700 AV. J. MILLER PRE-CAMBRL\N FOLDING IN NORTH AMERICA 



It may be added that more corroborative literature is at hand, and that arti- 

 cles which have appeared since the paper was written nicely fall in, in the 

 pre-Cambrian trends given, with those merely inferred for the regions in ques- 

 tion. It should also be pointed out, as has been fully done in my paper, that 

 while the author speaks principally of the fold directions, the trend-lines of 

 the pre-Cambrian rocks there under discussion comprise not only the fold 

 directions, but also the direction of the foliation, schistosity, and of the major 

 axes of the batholiths, all of which phenomena form a causally connected 

 group. 



It should be remembered that these criteria, in a paper dealing with their 

 continental or even world-wide order of magnitude, can not be judged fairly 

 and properly from the study of a very limited area in the Adirondacks alone, 

 however thoroughly this may have been done. 



Professor Miller further points out that "the vast length of pre-Cambrian 

 time and the uncertainties of its divisions, as well as the difficulty in many 

 places of distinguishing rock structures which developed during pre-Cambrian 

 time from those produced by post-Cambrian diastrophism, are antagonistic to 

 any attempt to decipher the pre-Cambrian configuration of the continent." 

 These difficulties are fully recognized in the paper and stated as such ; but 

 since also the general parallelism of the greater subdivisions in the different 

 continents, of the northern hemisphere at least, is set forth following the 

 views of Adams, Kemp, Willis, and others, and it is further brought out that 

 the folding and its associated phenomena, as seen now in the pre-Cambrian 

 rocks, is the summation of that of all pre-Cambrian eras and is treated as 

 such ; the criticism is beyond the point. Pre-Cambrian and post-Cambrian 

 folding have been carefully separated in the paper, and areas where the latter 

 is evident have been omitted from the discussion. 



As the conclusions set forth in my paper are based on a great mass of data 

 scattered in the literature, they must stand or fall. I repeat, with the correct- 

 ness of the many observations there recorded and with those yet to be made. 

 All that T, therefore, ask is that these conclusions be given a fair and unbiased 

 trial by those engaged in the study of pre-Cambrian geology and paleogeogra- 

 phy, and I have no doubt that such will be granted by the great majority of 

 geologists. 



Prof. A. P. Coleman : The early pre-Cambrian rocks of Canada rep- 

 resent only the foundations of the original mountains. They have batho- 

 lithic forms and the schistose structures strike in all directions around 

 the great batholiths, but the batholiths themselves generally show an 

 elongation in a direction roughly parallel to the edges of the pre-Cam- 

 brian Shield. In northern Ontario the structures run usually from 

 north 50 to 80 degrees east. The ancient mountain ranges overlying the 

 batholiths probably ran in the direction shown by this trend in the 

 elongation of the batholiths. 



Miss Margaret Fuller: The results of a recent detailed field study 

 of the pre-Cambrian geology of the Front Eange in Colorado, from the 



