832 A TREATISE ON METAMORPHISM. 



The hematitic and limonitic shales produced in the zone of katamor- 

 phism, and especially in the belt of weathering, are so unlike the original 

 rocks from which they were derived that one would not be inclined to 

 believe that they were derived from ferriferous carbonates if the actual 

 transitions had not been traced at many localities." 



After the ferruginous shales and ferruginous cherts have developed 

 they may undergo still further alterations. For instance, the hematitic and 

 limonitic shales may, after having been formed, become deeply buried, and 

 thus pass into the zone of anamorphism. In this position they are in the 

 zone of dehydration, and this process will occur, especially if mass- 

 mechanical action takes place. Thus there are produced the banded 

 hematitic siliceous rocks known as jaspilites, which are merely banded 

 hematite and quartz rocks. In some of the bands the quartz is dominant, 

 in others the hematite is dominant, and in still others both are abundant. 

 In the quartz bands innumerable minute grains of quartz are stained by 

 still more numerous microscopic flakes of red oxide of iron. The iron oxide 

 bands usually include much quartz. In proportion as mass-mechanical 

 action is severe the rocks take on a strongly developed schistose structure, 

 due to the similar dimensional arrangement of the hematite flakes. From 

 the nearly pure iron-oxide bands, bands of hematite-schist are produced, the 

 hematite being in brilliant parallel flakes resembling flakes of mica. These 

 bands of hematite are similar to the solid specular ore bodies. 



Excellent illustrations of hematitic schists and jaspilites are furnished 

 by the upper horizon of the Lower Huronian of the Lake Superior region, 

 especially in the Marquette district. In this district, after the original iron 

 carbonate had formed, the upper part of the formation was subjected to 

 alteration in the belt of weathering on an extensive scale, and thus was 

 transformed to hematitic and limonitic shales. It was afterwards buried 

 under the great mass of deposits of the Upper Huronian, and thus passed 

 into the zone of anamorphism. Later with that series the ferruginous 



a Irving, E. I)., and Van Hise, C. R., ThePenokee iron-bearing series of Michigan and Wisconsin: 

 Mon. U. S. Geol. Survey, vol. 19, 1892, pp. 193, 201-202, 205, 253, 294. Clements, J. Morgan, and 

 Smyth, H. L., with W. S. Bayley and C. R. Van Hise, The Crystal Falls iron-bearing district of 

 Michigan: Mon. U. S. Geol. Survey, vol. 36, 1899, p. 62. Van Hise, C. R., with Bayley, W. S., and 

 Smyth, H. L., The Marquette iron-bearing district of Michigan: Mon. U. S. Geol. Survey, vol. 28, 

 1897, pp. 336-375. Bayley, W. S., The Menominee iron-bearing district of Michigan: Mon. U. S. 

 Geol. Survey, vol. 46, 1904, pp. 397, 466-46S. 



