GEOLOGICAL EXPLORATIONS AXD LITEEATUEE— 1879. 67 



by slates and mag-nesian schists. Bed X of Brooks is a layer of siliceous 

 ferrugiuous schists, from which, locally, silica has been removed, leavmg 

 deposits of soft ores. These ore bodies are noticed to be in those portions 

 of the series where the disturbance has been greatest. The (|uartzite and 

 jasper-conglomerates were also observed in many mines forming the hang- 

 ing walls of the ore bodies, but their significance was not realized by the 

 author any more fully than it was by Brooks. Below Bed V, which is 

 the lowest identified by the latter geologist, AYright places a cjuartzite and 

 a garnetiferous mica-schist. 



The author also reports the discovery of a series of sharp ridges 

 composed of serpentine, marble, magnesian schists, etc., about 3J miles 

 northeast of Ishpeming. The rocks are similar to those occuriing at 

 Presque Isle. 



WiCHMANN, Arthur. A microscopical study of some Huronian clay-slates. 

 Quart. Jour. Geol. Soc, Vol. XXXV, 1870, pages 15C-164. 



In this paper Wichmaun gives a detailed description of the slates of 

 the Marquette district. He divides them into clay-slates, " deposited ou the 

 upper strata of quartzite " (forming Bed XV of Brooks and Bed VIII of 

 Credner), and occurring also in the marble series (Bed V of both Brooks 

 and Credner), novaculites, and carbonaceous shales. The slates are simi- 

 lar to those of later periods. Often they contain small tourmaline and 

 hematite crystals. The novaculites are hard, brittle clay-slates containing 

 garnets and quartz. In the carbonaceous slates carbonaceous material is 

 present in large quantities, and crystalline components are absent. The 

 paper ends with a discussion as to the processes of formation of slates, 

 but reaches no decided conclusions. 



Irving. E. D. Xote on the stratigraphy of the Hurouiau series of uortheni 

 Wiscousiu : and on the equivalency of the Huronian of the Marquette and Penokee 

 districts. Am. Jour. Sci. (3), Vol. XVII, 1879, pages 393-398. 



In 1879 Professor Irving began his series of valuable contributions to 

 the geology of the IMarquette district with a note in which he calls attention 

 to errors in Brooks's scheme of equivalency for the strata of the different 



