REPORT OF THE DIRECTOR I9IO II5 



rocks, various uncertain gneisses, and an apparently sedimentary 

 series represented by quartzites, schists and crystalline limestones, 

 besides many rocks of merely local importance. The undoubtedly 

 igneous types, which are generally later than the ore-bearing forma- 

 tions proper, include granites, diorites, feldspar porphyries and 

 diabases, the last two occurring commonly in dikes that intersect 

 the magnetite bodies. Of the gneisses a varied assortment exists: 

 the prevailing members in vicinity of the ores are alkali feldspar- 

 quartz rocks of strongly cataclastic textures and belong to the 

 leptite group under the Swedish terminology. The use of the word 

 " leptite " in Sweden is explained in the foregoing article by Pro- 

 fessor Kemp. The term comprehends both granulite and the ex- 

 tremely dense halleflinta-gneiss. They range from granites to 

 diorites in composition, but prevailingly carry some free silica. The 

 nearest approach to this series in the Adirondacks is perhaps ^the 

 gneiss surrounding the Hammondville magnetites which has been 

 described by the writer.^ The rocks of more or less sedimentary 

 aspect seem to be relatively subordinate to those already mentioned, 

 yet they inclose some large ore bodies. Their field appearance 

 recalls the Grenville series of the Adirondacks. Of local prominence 

 are amphibolites, usually feldspathic and with biotite or pyroxene 

 and " skarn." (This very useful word is employed in Scandinavia 

 for the aggregates of dark minerals — chiefly hornblende, pyroxene, 

 biotite and garnet and their weathering products — that mark the 

 borders of the ore bodies or occur as a gangue to the metallic 

 minerals). As to the general method of distribution of the crystal- 

 line rocks in central Sweden, it may be said that the true granites 

 constitute great masses which appear on the map as more or less 

 rounded areas. The ore-bearing leptite and sedimentary rocks form 

 belts squeezed in between or winding about the granite areas. 



Grangesberg with its large bodies of apatitic magnetite stands 

 apart from the other mines of central Sweden which we visited. It 

 is rather allied, if any comparison be justifiable, to Gellivare and to 

 our own apatitic magnetite occurrences as exemplified by Mineville. 

 The resemblance lies not only in the mineral association peculiar 

 to the ores, but is reflected as well in the larger features of the 

 occurrence — the general uniformity of the surrounding gneisses, 

 their predominantly sodic character, and the presence of granitic 

 rocks, especially the pegmatites which border or interweave the ore 



1 Geology of the Adirondack Magnetic Iron Ores. N. Y. State Mtis. Bui. 

 119, 1908, p. 45-49. 



