244 J. F. KEMP— AFTER-EFFECTS OF IGNEOUS INTRUSION 



he drew the conclusion that voids would result equal to 29.7 per cent for 

 iron epidote, and 46.9 per cent for grossularite. When, however, early in 

 1905, it was almost simultaneously announced by Professor Lindgren, 23 

 from his observations in Morenci, Arizona, and myself from studies in 

 San Jose, Tamaulipas, Mexico, 24 that much or almost all of the supposed 

 grossularite or lime-alumina garnet of the zones was really andradite, the 

 lime- iron variety, it became practically impossible to believe. that so much 

 iron oxide had ever been originally in the limestone. When, moreover, 

 we realized the great size of associated bodies of magnetite and specular 

 hematite, the case was even stronger. There are not a few great bodies 

 of iron ore of this kind in the Cordilleran region; in fact, practically all 

 the iron ore thus far discovered in the West is on the contact of intrusive 

 rock and limestone. Besides the iron silicates and oxides, we have great 

 bodies of iron sulphide, sometimes with copper associated, sometimes with 

 other ores. The conclusion is irresistible that, from the cooling and 

 crystallizing intrusive mass, iron and other metalliferous salts, along with 

 silica, have been fed into the limestone wall-rock in vast quantities and 

 have produced alike the lime-silicate zones, the ore bodies of intergrown 

 magnetite and specular hematite, and the various sulphides. 



Some interesting reasoning has been carried out as to the form of iron 

 compound which was primarily yielded by the intrusive. Experience 

 around volcanic vents leads us at once to suspect ferrous or ferric chlo- 

 rides. The suggestion of iron haloid compounds was made by J. H. L. 

 Yogt in the last century, but the haloid compounds are rejected as a 

 serious factor in his joint text-book with Beyschlag and Krusch in 1910. 25 

 Iron carbonate in the presence of water finds greater favor. 



Leith and Harder, in their studies of the Iron Springs District of 

 southwestern Utah, 26 in 1908 write a reaction using ferrous chloride in 

 association with calcium carbonate and derive specularite. V. M. Gold- 

 schmidt, describing in 1910 the zones near Christiania, Norway, 27 looks 

 with favor on iron chloride and fluoride and gives a reaction of ferrous 

 fluoride and calcium carbonate for specularite, believing also in the possi- 

 bility of magnetite. In explaining zinc-blende deposits at the contacts, 

 zinc chloride is tentatively considered by Doctor Goldschmidt. 



All these speculative attempts to throw light on the chemistry of the 

 process find support in the demonstrated presence of hydrochloric acid, 

 common salt, salammoniac, and hydrofluoric acid in the analyses of emis- 

 sions from effusive sources. 



With respect to the silica, one would at once surmise haloid compounds 

 as well as forms of silicic acid. Its actual introduction from the igneous 



