288 University of California Publications in Geology [Vol. 13 



of mineral springs in general the waters are probably dilute and of 

 meteoric origin. At any rate it does not follow that the same sort 

 of solutions circulated through the rock pores to produce metasomatic 

 deposits. These latter phenomena belong in an entirely different 

 category. 



"When a fissure becomes sealed by a mineral vein, and the vein 

 continues to grow by marginal accretion, whatever conditions may 

 have existed there to direct the flow of mineral-bearing solutions, they 

 have been obliterated by the freezing of the vein to its walls, and its 

 penetration into them. After that stage is reached the hypothetical 

 waters are as free to move through the pores of the country rock in 

 all upward directions as along the sides of the sealed fissure. There 

 is no directive force in hydrostatic pressure. But if instead of 

 moving waters, we assume the means of mineral transportation to 

 be the force of diffusion, driving migrant ions along the capillary and 

 subcapillary passages of the rock, then precipitation will be a directive 

 force capable of compelling the limitation of the diffusing of the 

 metalliferous ions to the shortest available paths leading to the seats 

 of deposition. The feasibility of that process and its application to 

 vein genesis at Cobalt, I will attempt to make clear in the succeeding 

 paragraphs. 



General Role op Diffusion in Vein Genesis 



In approaching the subject of geological diffusion the first ques- 

 tion to be met is : How is diffiusion through large masses of rock 

 to be reconciled with our conception of the processes of geochemistry ? 

 High heat and pressure are of course involved, but we are very apt, 

 on account of our petty habits, to overlook the most important factor, 

 namely, that of time. In considering whether concentrations of 

 mineral have been effected chiefly by the mechanical circulation of 

 solutions or by the diffusion of solutes through relatively stagnant 

 solutions, one finds it easier to see efficacy in flowing ground water 

 than in the tedious slowness and seeming weakness of diffusion. Forty 

 thousand years is the time estimated by some authorities since the 

 continental glacier disappeared from Ontario, yet the glaciated sur- 

 face in many spots still retains its polish. Vastly larger figures are 

 used to represent the duration of the Pleistocene period; but that 

 period, in its entirety, is short as compared with other periods. If 

 diffusion is a slow and weak process, it might nevertheless, in the long 



