242 University of California Publications in Geology [Vol. 8 



attacked and replaced intruded and intrusive rock alike; that this process of 

 contact metamorphism, or the deposition of lime-silicates, continued for a very 

 long time with definite stages indicating changes in the metamorphosing solu- 

 tions. This much is established beyond question. 



"In this case, then, the common conception that contact metamorphism, or 

 the formation of lime-silicates, is due to the effect of solutions pressed out and 

 expelled from the immediately adjacent intrusive rock into the wall rock at the 

 time of its consolidation, is regarded as an elementary one, not corresponding 

 to the facts. In the course of a considerable field experience with these deposits, 

 moreover, the writer has seen none where this conception seemed to apply. 

 Much less is this the case with the metallic minerals associated with these lime- 

 silicate deposits. ' ' 



Here we have a conclusion directly contradictory of that of Lindgren 

 in which he refers to the contact metamorphie deposits of the Clifton- 

 Morenei district as "contemporaneous with the cooling and solidifica- 

 tion of the porphyry." 



Now if the view which Spurr expresses is correct, and it is sub- 

 stantiated by a great many observations, the hypothesis of magmatic 

 waters becomes far-fetched and difficult of acceptance. It throws us 

 back for the source of the solutions upon a residual differentiate far 

 in the depths, as Spurr holds. It fails to account for the restraint 

 of the magmatic waters till this residual stage is arrived at. It 

 assumes great depths for small intrusions which were probably 

 injected from narrow vents. And it fails to explain the peripheral 

 disposition of the ores deposited from the waters thus rising from a 

 presumably central residual reservoir. In short, while Spurr 's obser- 

 vational data appear to be sound, his speculation as to the relation of 

 the mineralizing solutions to magma differentiation are not very 

 convincing. The sequence of deposition in accordance with the law 

 of falling temperatures would hold as well for meteoric waters deriv- 

 ing their heat from the magma as for waters escaping from the magma. 

 The success of his hypothesis, like others that depend upon magmatic 

 waters, presupposes a reasonable disposal of the alternative possibility 

 of meteoric waters. 



Transmitted September 1, 1914. 



