OUARTZITE TONGUE AT REPUBLIC, MICH. 



685 



upon itself, and that the neutral surface of division between the 

 portion above, that was subjected to compression, and the por- 

 tion below, that underwent tension, lay well beneath the heavily 

 bedded quartzite. The part of the sheet above the neutral 

 surface was confined within a progressively narrowing space, to 

 which it had to accommodate itself by thickening the beds, by 

 plicating them, and also by relative movement of each bed on 

 that below it. That the accommodation thus necessitated by 



Fig. 2. — Section north of the Thompson Pit. A = Lower Marquette Jasper. B = 

 Conglomerate. C = Quartzite tongue. D = Breccia. E = Jasper Wedge. 

 F — Conglomerate. G = Quartzite. One inch = 20 feet. 



the mechanical conditions actually did take the form of slipping 

 along bedding planes, is, in the case of the quartzite, clearly 

 shown. 



IV. 



I will now consider the quartzite tongue. The best expo- 

 sures of the conglomerate at the base of the upper quartzite 

 tongue, the included jasper wedge, and the main mass of jasper, 

 including all contacts, may be seen on the natural cross-section 

 afforded by the breaking down of Republic Mountain north of 

 the Thompson pit. This section is represented in Figure 2, and 

 a sketch plan of the outcrops is given in Figure 3. The con- 

 glomerate at the base of the main mass of quartzite is exposed 

 on the steep western face of the bluff, from its north end almost 

 to No. 8 shaft. It holds pebbles of jasper, of banded jasper and 

 ore, of ore, and of quartz, which last with ferruginous matter 

 forms the cement. The jasper inclusions are often large and 

 angular, and in many cases it is difficult to see that they are 

 completely detached from the main jasper body of the tongue. 

 The conglomerate cement, which is largely made up of grains of 



