DISCUSSION 701 



Continental Divide eastward through the Valley of the Big Thompson 

 Eiver to the foothills^ may shed some light on the question of the pre- 

 Cambrian structure of the Cordilleran area. The pre-Cambrian consists 

 of a series of highly metamorphosed sediments, mainly schists, intruded 

 by two granites, with their accompanying wealth of pegmatites. The 

 structure is one of numerous batholiths, which have arched and meta- 

 morphosed the sediments in a long north-south belt, the more intense 

 metamorphism being near the center of the range and extending north 

 and south in a belt which grades eastward into a similar north-south 

 parallel belt of less intensely metamorphosed rocks. This would indi- 

 cate that the original pre-Cambrian structure had been one of linear in- 

 trusion lines, arching up a north-to-south area. Similar structure in the 

 region north and west of Colorado Springs suggests the same conditions. 

 Probably the more recent arching, which uplifted the Front Range as it 

 lies today, took place along the old pre-Cambrian line of diastrdphism. 



Reply by Professor Miller : I regret that Dr. Ruedemann is not here 

 in person. His discussion, based entirely upon the very meager state- 

 ments in the abstract of my paper, would, I believe, have been consider- 

 ably modified had he heard my paper in full. 



In his paper (page 75) Dr. Ruedemann states it is an established fact 

 that the Archean basement complex has undergone complete meta- 

 morphism. I differ from him on this point, but I agree with him that 

 this matter is not necessarily of critical importance, as shown in my paper. 



In the second point of his discussion Dr. Ruedemann implies that my 

 whole field of experience is the Adirondacks, but this is by no means 

 true. He also states that all geologists, except myself, who have worked 

 in the Adirondacks agree to the proposition that the whole Adirondack 

 region has been severely folded. This is hardly a fair statement of the 

 situation, because, in the first place, I myself accepted the idea of severe 

 folding and compression of the region until about ten years ago, when I 

 began to critically examine the field evidence, and, in the second place, 

 some of the workers he cites studied only the northwestern flank of the 

 Adirondack region, where I, too, believe there has been more or less fold- 

 ing; some of the workers have never seriously argued for severe folding, 

 and only two of them have recently really advocated a severe folding of 

 the whole region. Now, as set forth in my paper, it is not a foregone 

 conclusion that the two workers who have advocated severe folding are 

 right and that I am wrong, certainly not in view of the fact that the 

 array of evidence presented by me in 11)16 (Journal of Geology, volume 

 24, pages 587-619) has not been attacked. The fact that I have done a 

 greater amount of detailed field-work on the pre-Cambrian rocks of 



