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SCIENCE 



[N. S. Vol. XXVI. No. 665 



mineralogy of granites and syenites, with 

 gneisses of doubtful relationships, and 

 with the schists and limestones of the sedi- 

 mentary (Grenville) type. Their origin is 

 obscure, a problem that has been fruitful 

 in discussion and theorizing among geolo- 

 gists. It is doubtful if any one of the ex- 

 planations that have been advanced is satis- 

 factory as a general basis for the whole 

 group ; rather it would seem that the vary- 

 ing conditions surrounding the character 

 and associations of the deposits indicate 

 that they have been formed by a com- 

 plexity of processes which may have dif- 

 fered materially in individual cases. 



The titaniferous magnetites are distin- 

 guished from those of the preceding group 

 by their higher percentage of titanium, 

 which ranges from about 3 or 4 per cent. 

 as a minimum up to a maximum of 10 or 

 15 per cent., and by the fact that they are 

 always enclosed by basic igneous rocks of 

 the gabbro family. They have been de- 

 scribed by Professor J. F. Kemp as basic 

 segregations formed during the cooling and 

 consolidation of the wall rocks, an explana- 

 tion that is generally regarded as correct. 

 Some of the largest deposits of iron ores 

 in the region belong to this class, those of 

 Lake Sanford being specially extensive. 

 After a long period of inactivity, due to 

 the difficulties encountered in smelting the 

 ores in the blast furnaces, attention is now 

 being directed to the deposits with a view 

 to their utilization. It has been found that 

 the ores in some cases at least are not 

 simply magnetite carrying titanium uni- 

 formly through its mass, but that they con- 

 sist of a mixture of magnetite and ilmenite, 

 the former having almost no titanium, a 

 condition that is favorable to their com- 

 mercial treatment. 



The hematite ores are practically limited 

 to the western Adirondack region of St. 

 Lawrence and Jefferson counties. In this 

 area the Grenville schists and limestones 



attain wide development, forming an inter- 

 bedded series which has been upturned 

 and sharply folded. Granite intrusions 

 are numerous, but there is a noticeable lack 

 of the basic igneous rocks that occur 

 abundantly in the central and eastern Adi- 

 rondacks. The ore bodies consist of lentic- 

 ular, tabular, or irregular masses enclosed 

 within belts of the schist and limestone, or 

 lying along the contact of these rocks as 

 at the Caledonia mine. Stringers and 

 larger bands of ore often extend out from 

 the main bodies for considerable distances 

 into the foot and hanging walls. The de- 

 posits have originated, without much 

 doubt, by a process of replacement. They 

 grade at the borders into the wall rock 

 and frequently inclusions may be found 

 that show complete transition from the 

 rock to the ore. Where the walls are 

 schist, the ore often preserves the appear- 

 ance of banding and cleavage, and not 

 uncommonly carries a small percentage of 

 graphite, the only mineral that seems to 

 have successfully resisted the solvent ac- 

 tion of the iron-bearing solutions. 



As to the source from which the iron has 

 come, the explanation advanced by C. H. 

 Smyth, Jr., merits full acceptance since it 

 meets the conditions surrounding the geol- 

 ogy of the deposits. His theory is that the 

 iron has been derived from pyrite and 

 magnetite, which occur abundantly in the 

 schist in the immediate vicinity of the ore 

 bodies. By oxidation the pyrite would 

 yield ferrous and ferric sulphates, which 

 would be readily taken up by the under- 

 ground circulations. Free sulphuric acid 

 would also result and react upon the veins 

 and disseminations of magnetite. By re- 

 action with the limestone and the minerals 

 of the schist, the solutions would decom- 

 pose and the iron precipitate as carbonate 

 and limonite. By subsequent alteration 

 these minerals have been changed to hema- 

 tite. Eesidual masses of carbonate are oc- 



