320 Notices respecting New Books. 



former area is bordered by Lake Superior, between Minnesota and 

 Michigan ; the latter, with a part of the iron district of Michigau 

 annexed, is traversed by the Menoninee River and some of its 

 affluents. 



Part I. of this volume consists of valuable observations by Pro- 

 fessor Poland D. Irving on the " General Geology of the Lake- 

 Superior Eegion,*' which is estimated at 70,000 square miles in area, 

 with strata, probably more than 100,000 feet in thickness, including 

 four great unconformable systems ; and the whole is coated with 

 enormous deposits of glacial drift, besides lake-alluviunis. I. The 

 Laurentian gneiss forms the crystalline nucleus of the region, 

 and is continuous with that of Canada. "With some associated 

 and often gneissoid granite, these altered strata are greatly folded, 

 and have a general southerly dip, with an E.-W. strike, and an 

 enormous thickness. II. The Huronian rocks are 12,800 feet 

 thick, and consist of (from below upwards): — 1. crystalline tremo- 

 litic limestone and a partial quartzite, 130 feet ; 2. quartz-schist, 

 mica-schist, and some novaculite, 410 feet ; 3. tremolitic magnetite- 

 schists and irony quartzites (Penokee Iron Range), 780 feet; 4. black 

 mica-slates, with diorite and schistose quartzites, &c, 3495 feet ; 

 5. dark -grey mica-schists, with intrusive granite, 7985 feet. The dip 

 is northward, and the strike is oblique to that of underlying Lau- 

 rentians. III. The Keweenawan or Copper-bearing series succeeds, 

 seven miles in thickness, and consists of distinctly stratified igneous 

 rocks like great flows and ash -beds. The lower rocks, from 10,000 

 to 30,000 feet, are almost wholly augite-plagioclase — namely, dia- 

 base, melaphyr, and gabbro (Eosenbusch). Shales, sandstones, and 

 conglomerates then come iu , and, becoming more and more frequent, 

 nearly exclude the igneous rocks for the uppermost 15,000 feet of 

 the series. IV. Lying on the ei^oded surface of the Keweenawan 

 strata is a great horizontal set of sandstones, defined as the " Lake- 

 Superior Sandstone,"' and regarded as equivalent to the Potsdam 

 Sandstone of the Mississippi valley. 



In Part II. Professor Eaphael Pumpelly gives the " Lithology 

 of the Keweenawan System," specimens of which were sent to him, 

 and represented Diabase, Melaphyr, Gabbro, UraLitic Gabbro, 

 Uralitic Diabase, Augite-diorite, and Felsitic Porphyries. 



Part III., by Prof. E. D. Irving, describes the "Geology of the 

 Eastern Lake-Superior District " of Wisconsin, premising its Topo- 

 graphy, with Altitudes, Drainage-system, A 7 egetation, and Soils. 

 The lithology, stratification, and economics of each of the great 

 systems are given in detail according to locality ; also an account 

 of the Glacial Drift and Lacustrine Clays (Champlain Series). 



Part IV., by Mr. C. E. Wright, treats of the " Huronian Series 

 West of Penokee Gap." The Penokee Iron Eange is here espe- 

 cially described, with the details of method of examination. The 

 magnetic bands being covered by Drift, their breadth and extent 

 were defined by the use of the solar dial-coinpass and the dipping 

 needle, both of which are succinctly described. The iron-ores are, 

 it seems, nearly all poor or "lean," the good ore being probably 

 high up in the series. 



