PLATE VI. 



FlGunE 25. (page 51) shows in section the relation of the "soft hematite," repre- 

 sented by oval marks, to the jasper and ore above and on both sides of it ; also to fis- 

 sures which allow the percolation of water, the upper portion of the figure being 

 adjacent to the surface of the ground. McComber Mine, Kegaunee. 



Figure 26 (page 55) shows in section reddish eruptive granite cutting gray gneiss. 

 The granite at the left and bottom of the figure is connected with the main body of 

 the granite. South of Ishpeming. 



Figure 27 (page 113) represents in section a tongue of trap extending down into 

 the ash-bed, and holding a rounded fragment of the latter. End of drift, Sept. 12, 

 1879, 5tli level. Copper Falls Mine, Keweenaw Point. 



Figure 28 (page 113) shows the denuded and irregular surface of the underlying 

 sandstone, covered by the overlying lava flow. Emerson Adit, Copper Falls Jline, 

 Keweenaw Point. 



All the figures, except when otherwise stated, are from free-hand sketches made in 

 the field from actual observed occurrences. 'So attempt has been made to draw to 

 scale, or to show anything except the actual relations of the rocks to one another. 

 The sketches were redrawn by the writer, engraved on stone by Jlr. L. Trouvelot, 

 and printed by A. Meisel. 



