86 PROCEEDINGS OF THE BALTIMORE MEETING 



Whatever the validity of the speculative suggestions may be, it is believed 

 that the recognition of the rotated, upthrust mountain block in place of the 

 currently accepted normal fault-block vt^ill advance our understanding of the 

 Pacific ranges. 



In the paper due recognition is given to the work of Gilbert, Le Conte, 

 Diller, Lindgren, Becker, and others in this field, and also to Barren's studies 

 of the conditions existing in the lithosphere. 



Presented by the author without notes. 



Discussion 



Dr. R. T. Chamberlin : I have been very much interested in this new ex- 

 planation advanced by Doctor Willis for the structure of these perplexing 

 Pacific ranges. Some experimental studies which I have been carrying on 

 have developed somewhat similar structures, and for their bearing on this 

 problem may perhaps be mentioned. In these studies blocks of various ma- 

 terials were subjected to various compressive stresses from two opposite sides 

 to determine the nature of fracturing. When rotational strains were devel- 

 oped, it was observed, in not a few cases, that the planes of fracture turned 

 sharply upward as they neared the upper surface of the blocks. In these 

 cases the fault-plane, which was nearly horizontal in the middle of a block, 

 curved and reached the upper surface as a nearly vertical plane, thus mani- 

 festing a rather striking resemblance to the diagram presented by Doctor 

 Willis. These results were noted in blocks of pure paraffine and other homo- 

 geneous materials, as well as in bedded strata, indicating that this behavior 

 of the fault-plane may take place independently of the nature or special struc- 

 ture of the material if the strain is of the proper sort. Because of the simi- 

 larity of these experimental fractures, though on a very small scale, to the 

 curving fracture planes just presented, I venture to mention them as having 

 a possible bearing on the problem. 



Mr. A. Keith : I have observed for years in the Appalachians certain facts 

 that accord with Professor Willis's analysis of the Pacific Coast structure. 

 The rocks in the Appalachians that are known to have been most deeply 

 buried have in very many cases a nearly flat foliation. Another major fact 

 in the Appalachians is the association of many great flat overthrusts with 

 flatly foliated gneiss or granite. It has long seemed to me that there is a close 

 association in cause between the great flat thrusts and the flat foliation due 

 to deep burial. 



Dr. G. R. Mansfield: Curved fault-planes are recognized in the Rocky 

 Mountain region along the Idaho-Wyoming border. The Bannock overthrust, 

 with gentle southwesterly dip, shows in places a pronounced upturning. In 

 several places dip even becomes southeasterly. 



Dr. G. W. Stose : I have been trying to understand the mechanics of the 

 diagram and how its operation will produce the results at the surface ascribed 

 to it. It seems to me that movement of a block on an arc of a circle of one 

 hundred miles radius would not tilt the surface of the block as stated. 



Remarks were also made by Professors H. F. Reid and J. P. Iddings^ 

 with reply by the author to questions raised by Professor Reid. 



