29!)
��kontinate membpr of the Serra do Mar syBtem (tlie SetT* da Bocaina, nr Quebra Cangalha), which, bein;; intercalat»l between the maritime range and theSeim ila Mftntiqueira, impels the river to the south, uiiiil, esrapiog around the end of this liarrier, it encounters another In the Hantiqueira. which forces it north- ward until it finds a pataase ftcross the Serrodo Har, and escapes to the sea. The Iguape, or Kibeira, in southern Sao Paulo, with its northern tributary liie Juquid, reveals the same fact of the Bplliting-itii of Ibe maritime range into distinct ridges.
O. A, Dbhbv.
��^■' Ik liis Opening chapter, Professor Irving gives a succinct history of the earlier investi- gations of the cop per- bearing locks of Lake Superior, a clear exposition of the views that bave been held respecting them, and a full bibliography of his sul>jei.-t. The <lisciiasioii proper is introduceil by a sketch of the e.xtent nnd lending characters of the forruation, illiis- trated by an excclleut map. This is the first really synoptical view of the series, in any thing like its regional entirety, that has been preseuted.
Instead of a mere local phase of some well- known geological horizon, it is doseiibed as a unique formation of consistent characters and enormon 3 thickness, stretching out to an ascer- tained length of live hundred miles, with u width of a hundred miles, and an area, ex- clnding the Nipigon extension in Canada, of forty-one thousand sijuare miles, — nearlj- 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 .ind cou- glooierates, and over which lies a great thick- ness (liflccn thousand feet) of detrital material, making a total pile of forty thousand feet.
A careful description of these rocks next follows, illustrated by very line 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 Puuipelly in llie 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
iloHographM of tht I'. S.eeiilMlcal ™rMy. Fnl.: Tlit cep- prr-btartng nrlu tf Lakr .Sunrrhr. By Roland UiTsalBTiHa. ^■tmbmgtoB, Guttrnmnl, im. 18-4W p.,ai pl..37 Btpi. 4-.
��interesting anoilliile rock. To the acid crup- tives he has made a more notable contribution in determining not only the presence, which was partially known before, but the imi>ortant development of quartzless porphyries. (|iiartz- iferous |>orphyries. felsites. augite syenites, granitells. and granites. He shows that these are, at the same time, membci-s of the original eruptives, and chief contributors to the detri- tal beds, es|>ecially the couglo me rates. But more completely new and theoretically impor- tant is the recognition of a elaas of interme- diate rocks (silica from fifty-two to sixty per cent) which constitute phases of the orthoclose. uralitic, and hornblende gabbros. and of the diabases, diabase porphjiies, and llieir amyg- daloidal forms. The detiital rocks are con- glomerates and sandstones, with shaly phases. Thej' 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 arc 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 devoU-'d to the stratigraphy of the .'series. The autiior maintains with justness, that the igneous lieds, being overflow sheets, are fully amenable to the common laws of stratigraphy: and hts discussion is nolahly 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 be inaugurates a new era in the discussion of Lake-.Superior geology, in which the study of its problems shall be cosmoiKtlitan, in distinction from that narrow provincialism or that distant iin familiarity which has so largely vexed their past history. Pi-ofessor Irving's descriptions necessarily fall much short of full completeness; but they con- stitute a great advance in the endeavor to give, b}' 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 scries to the associated formations, and traverses the ground which has been most contested in Lake-
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