64 rROCEEDINGS OF THE CHICAGO MEETING 



one, much discussed for many years. Any light wliich may be thrown on the 

 problem by a study of the Adirondack magnetites is of special interest, be- 

 cause they comprise some of the most important deposits on the continent, 

 especially those now being worked at Mineville and Lyon Mountain and in the 

 abandoned mines at Hammondville. Most of the important mines have been 

 visited by the writer. 



According to the writer's theory, a gabbro or metagabbro older than the 

 great syenite-granite series was the main or sole source of the magnetite de- 

 posits, and the derivation of the ore from the gabbro and its concentration 

 into large deposits was accomplished by the intrusion of the syenite-granite 

 magma, more especially its residual pegmatitic and silexitic portions, rich in 

 hot gases, vapors, and fluids (mostly water). 



The almost, if not quite, constant direct association of the non-titaniferous 

 magnetic iron ores throughout the Adirondacks with granite, particularly 

 where it is rich in pegmatite or silexite, and an older metagabbro (in many 

 cases more or less thoroughly injected or assimilated) is a fact which can not 

 be too strongly emphasized. One of Newland's main criticisms is that "admix- 

 ture (of the granite) with foreign material seems to have no bearing on the 

 distribution of the ores in general," except to some extent in the Lyon Moun- 

 tain district. With this statement the writer flatly disagrees, and this dis- 

 agreement is based on a great many observations made at magnetite localities 

 throughout the Adirondack region during the last fourteen years. 



Newland is very skeptical in regard to the derivation of the ore from the 

 old gabbro and says that convincing quantitative evidence is lacking, and this 

 in spite of the fact that detailed statements, backed up by chemical analyses, 

 are presented in the writer's paper. Field studies, supported by study of many 

 thin sections, shows that, in and around the ore deposits, tremendous quanti- 

 ties of iron-poor diallage have resulted from transformation of the iron-rich 

 minerals of the old gabbro by the action of the granite magma and pegmatite. 

 Obviously, then, large amounts of iron oxide were set free. But what became 

 of so much iron oxide? According to the writer's theory, it was taken up in 

 the pegmatitic solutions, carried along, usually not very far, and concentrated 

 as ore deposits. How would Newland answer this question? 



Newland thinks there is no difficulty in the way of explaining the ore de- 

 posits as magmatic segregations in the granite itself. If the ores are straight 

 magmatic segregation deposit of the granite, why did not at least some de- 

 posits of considerable size develop well within portions of the granite free 

 from admixture with old gabbro? 



PreseiitGcl by title in the absence of the author. 



MAOyETlTES OF NORTH CAROLINA — THEIR ORIGIN 

 BY WILLIAM SHIRLEY BAYLEY 



(Abstract) 



In his discussion of the magnetite ore at Cranberry, North Carolina, Mr. 

 Keith ascribed its origin to solution emanating from the "Bakersville gabbro,"' 

 which he believed to be of Juratrias age. In the summer of 1919 the magnet- 



