58 TUH MAliQUETTE IltON-BEAKING DISTRICT. 



give a soiiit'wliat popular description of such cliaractcristics of the common 

 varieties [of tlie Marquette rocks] as may l)e easily discerned (with a very 

 few exceptions) in the field, * * * and also to propose a temporary 

 nomenclature and classification for the present use of your report." 



The rocks are divided into three great divisions, the simple rocks, the 

 mixed crvstalline rocks, and the fragmental rocks. The first division is 

 subdivided into calcareous, quartzose, silicate, iron ore, and carbonaceous 

 rocks, and the mixed crvstalline rocks into older and younger feldspathic 

 rocks. The former includes granites, gneisses, mica-schists, greenstones, and 

 traiipean diorites, and the latter only diorite-aphanite. The fragmental rocks 

 examined were sandstone-schists. 



The greenstones comprise diorite, amphibolite, serpentine, chloritic dio- 

 rite, diorite-wacke, diorite-schist, amphiljole-schist, diorite-greenstone, mica- 

 ceous greenstone-schist, schalstone, aphanite-schist, and chlorite-potstone. 

 All these varieties are supposed to be derivatives of diorite, and none of 

 them were believed to be derived from diabase. "I am decidedly of the 

 opinion," writes Julien, "that no augite occurs in these rocks, and that there 

 is no diabase whatever in this region" (p. 42). The trappean diorite and 

 the diorite-aphanite are intrusive basic rocks, but according to the author 

 the^s' contain no pyroxene. 



The simple silicate rocks determined are amphibolite, amphibole-schist, 

 hornblende-schist, anthophyllite-schist, chloritic schist, argillite, and talcose 

 schist. The argillites are placed in this division rather than among the 

 fragmental rocks because some of them were believed to be composed of 

 greenstone (diorite) ash. 



A few mineralogical notes close the report. 



Bkooks, T. B., and Julien, A. A. Catalogue of the Micbigan State collection 

 of the Hurouiaii rocks and associated ores. Geol. Surv. of Michigan, 1869-1873, 

 Appendix B, Vol. II, Xew York, 1873, pages 199-21:2. 



The second appendix is a classified list of the collections of Michigan 

 rocks distriltuted by the State to certain colleges and institutions in this 

 country and abroad. 



