392 THE MAEQUETTE lEON-BEAEIXG DISTKICT. 



within the iron-bearing formation, and (3) those at the top of the iron- 

 bearing- formation. (PL XXVIII, fig. 1.) By the last is meant the horizon 

 immediately behiw the next overlying formation, the Goodrich quartzite. 

 The ore deposits of the second ciass frequently reach the surface, but are 

 not at the uppermost horizon of the formation. The first two classes 

 of ores are generally soft, and the adjacent rock is ferruginous chert or 

 "soft-ore jasper" (Pis. XX-XXII), while those at the top of the iron- 

 bearing formations are hard specular ores or magnetite, and the adjacent 

 rock is jaspilite, also called "specular jasper" and "hard-ore jasper" 

 (Pis. XXIII-XXVII). This last class of deposit frequently runs up, past 

 the unconformity, into the Upper Marquette Goodrich quartzite, and some- 

 times some of these ore bodies are almost wholly in this position. Strati- 

 graphically the consideration of these deposits ought to be deferred until the 

 Goodrich quartzite is treated, but they are so closely connected genetically 

 and in position with the Lower Marquette ore deposits that they are here 

 treated. 



While the larger number of ore bodies can be referred to one or another 

 of these three classes, it not infrequently happens that the same ore deposit 

 belongs partly in one and partly in another. To illustrate: The inter- 

 Mar(][uette erosion may have cut so nearly through the iron formation 

 that an ore deposit may extend from the bottom of the formation to the 

 top. However, in these cases the ore bodies are usually hard, and, upon 

 the whole, are more closely allied to the third class than to the first. In 

 miany places, also, the upper part of an ore deposit may be at the topmost 

 horizon of the iron-liearing formation, and be a specular ore, while the 

 lower part is wholly within the iron-bearing fonnation and is soft ore. In 

 some places there is a gradation between the two phases of such a deposit, 

 but in more instances the two bodies are separated by a dike, now changed 

 to soapstone or paint-rock. 



(1) The ore deposits at the bottom horizon (PL XXIX, figs. 3 and 4) 

 c^n occur only where the lowest horizon of the formation is present; that 

 is, they are confined to that part of the formation resting upon the Siamo 

 slate or the Ajibik quartzite. Hence they are found along the outer 

 borders of the formation, and do not occur in the broad Ishj^eming-Negaunee 



