1922] Whitman: Genesis of the Ores of the Cobalt District 287 



must materially detract from the weight of the argument that volcanic 

 phenomena indicate the presence of large quantities of water in 

 magmas, and that batholithic or laccolithic masses may be presumed 

 to exhale considerable quantities of it either before or after crystal- 

 lizing. 



The phenomena of aureoles about igneous masses and of pegmatitic 

 offshoots are usually interpreted as indicating the escape of juvenile 

 waters from the magma. Some mineral springs may be placed in the 

 same class of evidence. In mineral springs we have to account for 

 mineral, heat, and water. Lindgren indicates in the above quotations 

 his suspicion that vadose water may greatly augment the volume of 

 such springs ; and Lawson points out convincingly that such springs 

 may not only be augmented by additions of vadose water, but that 

 almost the entire volume may be meteoric, having passed through 

 fissures in the igneous mass itself, arriving there through fissure con- 

 duits from distant sources. All parties agree that the heat and 

 mineral content may be of igneous origin ; but that argues nothing 

 relative to the passage of large quantities of juvenile, or of meteoric 

 water either, for that matter, through rock pores. Even pegmatitic 

 and pneumatolitic phenomena argue nothing as to volumes of water. 

 They merely indicate transfers of material. Their transitions in min- 

 eral content and various other evidences point strongly to a fluid 

 medium of transfer, but neither to its volume nor to the duration of 

 the process of dike and vein formation. The dikes appear in many 

 cases to occupy fissures, but in others there is a vague transition from 

 pegmatite to mother rock. The material may have been expelled from 

 the igneous source in a single short interval, along a fissure; and the 

 excretion may have been a very rich liquor of comparatively small 

 volume. In any case there is no sound evidence of long continuance 

 of the process, nor of the issuance of large quantities of water such 

 as would be implied in the idea that these phenomena were connected 

 with hot springs. The same holds for aureole phenomena. The 

 assumption of large emanations of water is unwarranted. There 

 may be a way of understanding the migration of material without 

 recourse to the postulation either of the escape of considerable quan- 

 tities of water from an igneous mass or of its passage through rock 

 pores. 



Crustified veins may be regarded as good evidence of the passage 

 of large volumes of hot mineral-bearing waters through open chan- 

 nels, issuing at the surface as mineral springs ; but here as in the case 



