THE IIEPUBLIC THOUGH. 543 



this sino'iilav fact was given by Brooks in the text of the Michigan report. 

 Wadsworth' has hxtelv endeavored to expLain these rehitions by the assump- 

 tion that the wedge of the specuhar jasper included l^etween the two quartz- 

 ites does not belong to the lower series, but to the ui)per, and was deposited 

 later than the quartzite tongue. It is believed, however, that the phenomena 

 are really due to faulting. (PI. XXXIV, fig. 2.) 



The best exposures of the two quartzites, the included jasper, and the 

 underlving iron formation of the lower series, with all the contacts, may be 

 seen on the natural cross-section aiforded by the breaking down of Republic 

 Mountain north of the Thompson pit. The conglomerate at the base of the 

 main mass of the quarztite is exposed on the steep western face of the bluif. 

 It holds pebbles of red jasper, of jasper banded with ore, of ore, and of 

 quartz, which last, with ferruginous matter, forms the cement. The jasper 

 inclusions are large, many of them are angular, and near the contact small 

 quartz grains fill irregular cracks in the underlying jasper tongue. The 

 conglomerate is distinctly basal, and unquestionably was laid down on an 

 eroded surface. From this contact, for about 16 feet to the east, the jasper 

 tono-ue comes in. This rock is greatly brecciated, but it contains no mix- 

 ture of foreign fragmental material. To the eye and under the microscope 

 it is not to be distinguished from the ordinary specular jasper of the under- 

 lying iron formation. For the next 5 feet occurs a mixture of large angular 

 pieces of jasper (one measured 3 feet by 1 foot), of quartz, and probably 

 quartzite, many somewhat rounded pebble-like forms of all these, and much 

 siliceous cement. About 6 feet of westeriy dipping quartzite, constituting 

 the quartzite tongue, follow, and then come 3 to 4 feet of conglomerate, 

 entirely similar to the first conglomerate and having similar relations to the 

 specular jasper, which continues in an unbroken body to the east. 



The significant facts at this contact, which seem clearly fatal to the idea 

 that the jasper is an interbedded member of the upper series, are these: 

 The conglomerate at the base of the main quartzite is as cleariy separated 

 from the jasper wedge by an erosion interval as the conglomerate below the 

 quartzite tongue is from the main mass of specular jasper. The jasper 



' Report of the State Board of Geological Survey, Lansing, 1893, pp. 129-130. 



