1922] Hudson: Geology of the Cuyamaca Region of California 241 



of two processes: either (1) two immiscible liquids, copper and sul- 

 phide, were present prior to solidification, and the copper persisted 

 in the molten condition after the solidification of the sulphide, and was 

 thus able to vein the sulphide, or (2) a solid solution of copper in 

 substance "D," stable at the temperature of consolidation, broke 

 down as the matte cooled. 



Fulton and Goodner have observed the sudden appearance of ' ' moss 

 copper ' ' in mattes of comparatively low copper content when the matte 

 was nearly cold but still too hot to bear the hand upon it. They sug- 

 gest that the dimorphic point, 103° C, marks the throwing out of 

 metallic copper from solution in the Cu 2 S — FeS. 78 If this be so, 

 then the second of the two processes suggested in the previous para- 

 graph is probably the correct one. 



The "veining" of one constituent of cast manganese steel by other 

 constituents is well shown in photographs presented by Potter 77 and 

 Young, Pease and Strand. 78 These are reproduced as plate 13, figures 

 3 and 4 of the present report, together with two photographs of 

 Sudbury ores (plate 5, figures 2 and 5) whose textures are much like 

 those of the alloys. It is obvious that the veins in the manganese steel 

 do not prove that the ferrite or the troostite were introduced from 

 without after the solidification of the ground mass. 



To the writer all these things go to show that veinlike forms of 

 one mineral within another do not prove that the "vein mineral" was 

 introduced from without, replacing the "previously formed" minerals. 

 Neither can we assume that in all cases the "vein mineral" was molten 

 after the solidification of the ground mass. 



It is thought, then, that the conclusions of Tolman and Rogers, 

 and Campbell, and Knight, based on the minute textural relations of 

 the minerals, rest on very insecure foundation. 



Without doubt there has been introduction of material from without 

 after the primary ore formation in many of the magmatic ore deposits. 



It is thought that in many such deposits the secondary action has 

 masked the primary relationships. In such cases conclusions as to 

 origin must be based on large scale geologic relations, just as Vogt, 

 Barlow, Bell, Coleman, and many others have urged. 



In the case of the Friday Mine deposit the absence of veining is 

 considered as corroborative evidence pointing to syngenetic magmatic 

 origin. 



76 Fulton, C. IL, and Goodner, I. E., A. I. M. E., Trans., vol. 39 (1908), p. 618. 

 " Potter, W. S., A. I. M. E., Trans., vol. 50 (1914), p. 465. 

 78 Young, Pease and Strand, ibid., vol. 50 (1914), p. 427. 



