226 THE MARQUETTE IRON-BEARING DISTRICT. 



is scattered through th(» honiogeneous quartzose background somewhat uni- 

 formly. The major })art of tlie supposed quartzite pebbles, as seen in liand 

 specimen, are found to be com])lex interlocking quartz and much mashed 

 and broken quartz-schist, in which a great deal of secondary quartz has inlil- 

 trated. In a less mashed phase the quartz is in distinct, closely fitting or 

 interlockiua' ffranules, which suffsrest a frag-mental character, but althoug-h 

 carefully searched for, no evidence could be found of enlargement or of 

 cores, and it is probable tliat the material is from veins. The chert, jasper, 

 and quartz pebbles may have been derived from veins in pre-i\[arquette 

 rocks, or possibly in part by the mechanical destruction of secondary veins 

 within the formation itself 



The matrix of these conglomerates consists of quartz and feldspar 

 fraginents, set in a background composed of more finely pulverized and 

 kaolinized materials of the same kind. , In man-\' cases also this back- 

 ground contains much very finely crystalline, cherty quartz. The slides 

 are also cut through l^y veins of the same cherty quartzose material. In 

 some cases dvnamic action has broken up the cherty matrix and chert 

 veins, producing pseudo-pebbles, and this may be the source of some of the 

 fragments which at first sight appear to have been derived from a pre- 

 existent cherty rock. The feldspar fragments frequently show interesting 

 micaceous and (juartzose decomposition. The quartz grains are often 

 enlarged. All of the grains, whether in the complex fragments or in the back- 

 ground, show undnlatorv extinction or fracturing. The same ])lienomena are 

 exhibited by the feldspars, but to a less degree. In certain cases the frac- 

 tures in the quartz are in two systems at right angles to each other, pro- 

 ducing many little rectangular ])articles of quartz from a single individual. 



At places near the base of the formation the much ma.shed, fine-grained 

 conglomerate can not in hand specimen be discriminated froni the gneiss 

 below. As seen in thin section, the fragmental rocks are found to be kao- 

 linic quartz-schists. The simjile and complex quartz grains usually show 

 distinct rounding, although some of them have a decided granitic shape. In 

 many slides they are granulated and greatly elongated in a common direc- 

 tion bv dvnamic action. Feldspar fragments, if present originallv, have 

 decomposed. The (quartz grains are in a matrix of finely crystalline, cherty 



