Plate XXI.— HEMATITIC CHERT FROM NEGAUNEE. 



The plate shows a somewhat different stage of alteration from PI. XX. The bands of chert are so 

 broken by movement that they are in some places difficult to follow. Many of the fragments 

 have roundish outlines, due to their partial solution and replacement by iron oxide. In the field 

 there may be found every phase of transition between the rock represented by fig. 1 of PI. XVII, 

 through the rocks represented by the figures of PI. XIX, to the rock rei>resented by fig. 2 of 

 PI. XX and to the varieties represented by PI. XXI. Fig. 2 represents a somewhat more 

 advanced stage of alteration than fig. 1. The material illustrated is frequently found very 

 close to the ore bodies. If a portion of the remaining silica were removed and iron oxides 

 introduced in its place, it would become iron ore. The hematite is soft, and the material 

 illustrated is therefore called soft-ore jasper by the miners. 

 348 



