April 10, 1885.] 



SCIENCE. 



299 



subordinate member of the Serra do Mar system (the 

 Serra da Bocaina, or Quebra Cangalha), which, being 

 intercalated between the maritime range and the Serra 

 da Mantiqueira, impels the river to the south, until, 

 escaping around the end of this barrier, it encounters 

 another in the Mantiqueira, which forces it north- 

 ward until it finds a passage across the Serra do Mar, 

 and escapes to the sea. The Iguape, or Eibeira, in 

 southern Sao Paulo, with its northern tributary the 

 Juquia, reveals the same fact of the splitting-up of 

 the maritime range into distinct ridges. 



O. A. Derby. 



IRVING ON THE COPPER-BEARING 

 ROCKS OF LAKE SUPERIOR. 



Ix his opening chapter, Professor Irving 

 gives a succinct histon r of the earlier investi- 

 gations of the copper-bearing rocks of Lake 

 Superior, a clear exposition of the views that 

 have been held respecting them, and a full 

 bibliography of his subject. The discussion 

 proper is introduced by a sketch of the extent 

 and leading characters of the formation, illus- 

 trated by an excellent map. This is the first 

 reall}' synoptical view of the series, in any- 

 thing like its regional entirety, that has been 

 presented. 



Instead of a mere local phase of some well- 

 known geological horizon, it is described as a 

 unique formation of consistent characters and 

 enormous thickness, stretching out to an ascer- 

 tained length of five hundred miles, with a 

 width of a hundred miles, and an area, ex- 

 cluding the Nipigon extension in Canada, of 

 forty-one thousand square miles, — nearly two- 

 thirds the size of New England. - ; Through- 

 out this wide extent, though local peculiarities 

 are to be noted, the general characteristics of 

 the group are wonderfully constant." It con- 

 sists of an enormous series of eruptive sheets, 

 — lava overflows in the main, — among which 

 are intercalated beds of sandstones and con- 

 glomerates, and over which lies a great thick- 

 ness (fifteen thousand feet) of detrital material, 

 making a total pile of forty thousand feet. 



A careful description of these rocks next 

 follows, illustrated b} 7 very fine microscopic 

 sections, and conveniently summarized in 

 tables. The studies of Professor Irving do 

 not add greatly to the kinds of basic rock 

 previously described by Professor Pumpelly in 

 the reports of Michigan and Wisconsin ; viz., 

 diabases, malaphyrs, and gabbros. He has, 

 however, amplified the varieties and the geo- 

 graphical distribution of these, and added an 



Monograph* of the U.S. geological survey. Vol. v. The cop- 

 per-bearing rock* of Lake Superior. By Roland Duer Irving. 

 Washington, Government, 1883. 16+464 p., 29 pi., 37 tigs. 4°. 



interesting anorthite rock. To the acid erup- 

 tives he has made a more notable contribution 

 in determining not only the presence, which 

 was partially known before, but the important 

 development of quartzless porphyries, quartz - 

 iferous porphyries, felsites, augite syenites, 

 granitells, and granites. He shows that these 

 are, at the same time, members of the original 

 eruptives, and chief contributors to the detri- 

 tal beds, especiall}' the conglomerates. But 

 more completely new and theoretically impor- 

 tant is the recognition of a class of interme- 

 diate rocks (silica from fifty-two to sixt}' per 

 cent) which constitute phases of the orthoclase. 

 uralitic, and hornblende gabbros. and of the 

 diabases, diabase porphyries, and their amyg- 

 daloidal forms. The detrital rocks are con- 

 glomerates and sandstones, with shaly phases. 

 They are chiefly derived from the acid erup- 

 tives, though where closely associated with 

 basic rocks, a large element is derived from 

 these. In some parts a notable contribution 

 has been made by the older crystalline rocks. 



The lithological discussions are critical, and 

 evince a familiarity with the latest phases of 

 this rapidly developing branch of study. They 

 embrace a hundred and eighteen pages. 



Following this are nearly two hundred pages 

 devoted to the stratigraphy of the series. The 

 author maintains with justness, that the igneous 

 beds, being overflow sheets, are fully amenable 

 to the common laws of stratigraplry ; and his 

 discussion is notably free from the license of 

 eruptive geology. He brings together for the 

 first time, from his own and others' observa- 

 tions, specific descriptions of the formation 

 from all sides of the Lake-Superior basin. It 

 is to be hoped that in this he inaugurates a new 

 era in the discussion of Lake-Superior geology, 

 in which the study of its problems shall be 

 cosmopolitan, in distinction from that narrow 

 provincialism or that distant unfamiliarit}' 

 which has so largely vexed their past history. 

 Professor Irving' s descriptions necessarily fall 

 much short of full completeness ; but they con- 

 stitute a great advance in the endeavor to give, 

 by precise descriptions, maps, and sections, 

 an approximately accurate conception of the 

 entire formation, so far as displayed in the 

 Superior region. Completeness will only be 

 approached when it is possible to extend over 

 the whole region such excellent detail work as 

 that of Pumpelly and Marvine in Michigan, 

 and the author himself in Wisconsin. 



The eighth chapter of the monograph is de- 

 voted to the relations of the Keweenaw series 

 to the associated formations, and traverses the 

 ground which has been most contested in Lake- 



