110 proceedings: geological society 



sibly one-third its area. It is safe to assume that the intrusion of this 

 material either caused or accompanied a profound elevation of the sur- 

 face; yet the area of granitic intrusions shows no significant relation to 

 surrounding sedimentary deposits until the Eocene. It is suggested, 

 therefore, that the granitic intrusions initiated or accompanied the 

 initiation of the cycle of erosion which resulted in the gentle topographic 

 forms of Eocene age. 



4. The Eocene erosion surface truncates the earlier mineral deposits. 

 On the other hand these are younger than the granite which encloses 

 some of them. They are therefore assigned to the late Cretaceous or 

 early Eocene. The later veins are enclosed in or associated with erup- 

 tive rocks which occupy valleys developed after the elevation of the 

 Eocene surface. Allowing the Oligocene period for the development of 

 these valleys and evaluating the amount of erosion that took place be- 

 tween the extravasation of the lavas and the beginning of the Pleisto- 

 cene, it is concluded that the younger veins are Miocene or early Plio- 

 cene. 



Mines and prospects of southwestern Oregon: J. S. Diller. This 

 paper presented the preliminary results of a study not yet completed, 

 which will later be embodied in a report by the Geological Survey. A 

 general geological map of northwest California and southwest Oregon 

 illustrated the distribution of the larger groups of formations and called 

 attention to the fact that the Sierra Nevada and Klamath Mountains 

 are composed in large measure of the same formations and that these 

 formations are closely allied also to those of the Blue Mountains of 

 eastern Oregon. All these mountains are important mining regions. 



The rocks of the Klamath Mountains have been subjected to vigorous 

 compressive stresses in two directions approximately at right angles to 

 each other. One set of stresses folding the rocks along axes running 

 northwest and southeast, and prevailing in the southwest portion of the 

 Klamath Mountains, connects them with the Sierra Nevada; the other 

 set of stresses folding the rocks along axes running southwest and north- 

 east, and prevailing in the northeast portion of the mountains, connect- 

 ing them with the Blue Mountains of Oregon. 



As a result of the divergent stresses there has been widespread crush- 

 ing on diverse lines among the rocks of the Klamath Mountains. Con- 

 sequently the later igneous intrusions with their mineralizing ore-bearing 

 solutions from within the earth found many scattered lines of egress 

 towards the surface, and the ore deposits, though abundant, represent 

 in general a low instead of a high degree of concentration. 



On a map of southwest Oregon was shown the location of the principal 

 gold and copper mines from the California line thru the Grant's Pass 

 region to Bohemia, and on a special sketch map was outlined the geology 

 and mines in the vicinity of Galice and Kerby. Attention was called 

 to the fact that the Galice slates contain fossils characteristic of the 

 Mother Lode district in California. 



Robert Anderson, Secretary. 



