Page:Science vol. 5.djvu/465

 Mat M. 1883.1

��reasons. The science of geolt^- has received no iDsigniticant coatribution in these pnblica- tioDs. Much light has been thrown upon some unsettled problems ; nnd if they are still unsettled, or if their solutions are still disputed, the conlribution is not less real, because the data afforded by the state are insutflcient bases lor positive conclusions. Each formation of the state has been carefully mapped ; its strati- gi'aphical relations determined ; and its fossils, when fossils exist, identified. Ninety-four new species are described and figured, as also are some of the more characteristic forms pre- viously known.

Among the more important and interesting results are the determinations which have been made respecting the subdivisions of the archaean formation, and those which pertain to glacial geology. Concerning the former, the Wisconsin geologists recognize three dis- tinct groups of rocks, — the Laurentian, Huro- nian, and Keweenawan. These groups, it is maintained, are not only distinct, but separated by inten-als which, in point of time, were of no inconsiderable duration, — intervals long enough in each case to allow profound changes, both stratigraphical and petrographical, to be accomplished during their continuance. The evidence cited in support of this subdivision, as well as that bearing on the distinctness of the Keweenawan from the Potsdam formation above, is of a positive and perfectly definite character. The greatest break is held to occur between the Laurentian and Iluronian series, The rooks of the Laurentian series are much more highly metamorphosed than those of the Huronian which overlie them; they are in a highly folded and contorted state, while the Euronian rocks have suffered notably less strati graphical distortion ; the laminations of the two series, when seen in contact or prox- imity, are discordant; the later series con- tains, at ila yery base, material from the older highly metamorphosed rocks ; and the relations of the two series to penetrating igneous rocks are such as to emphasize the conclusion to which the other lines of evidence point. Al- together, the evidence npon which the subdi- vision is based is strong, and, for the region under consideration, is certainly convincing. The separation of the Keweenawan rocks from the Huronian on the one hand, and from the Potsdam on the other, rests on scarcely less positive grounds. The question as to whether the Keweenawan group is to be classed as Cambrian or pre-Cambrian, is one concerning which there remaius room for doubt. In any event, the im]«jrlant fact developed is the exist-

��ence of a distinct formation younger than the Huronian, and unconformably subjac«nt to the oldest formation of the interior known to contain Cambrian fossils.

At the other end of the geological series equally important advances have been made. For the study of quaternary geology, Wiscon- sin is an exceptionally good field, because of the proximity of driftless. old-drid, and new-drill areas. The determination in 1.S74, of the morainic character of the previously known a new impetus to the study of the drift phenomena. Following this important deter- mination was the demonstration of the char- acter of ice-movement in a relatively level region, as exemplified by the ice which occupied the Green-Bay valley. The proof of the lobation of the ice-margin followed, and the facts anchs in the glacial period, separated, according to Professor Chamberlin, by an •interval which may not have been less than the time which has elapsed since the last. Although the existence of two ice- epochs is not yet universally admitted, the drift phenomena of Wisconsin, especially when con- sidered in connection with like phenomena throughout the interior, place the hypothesis upon a substantial basis. Although later in- vestigations have slightlj' modified the borders of the driftless area as mapped by the survey, the reality of its existence is beyond question ; and it is just as certain that between this area and that bounded by the Kettle Aforaine, which marks the limit of ice advanced in the second epoch, aa interpreted by Professor Chamberlin, there is an area covered with glacial drift, which, as indicated by the greater amount of erosion which it has sutt'cred. is of much less recent origin than that within the Kettle Moraine.
 * - Kettle Range ' of eastern Wisconsin, gave

The consideration of the ore-deposits of south-western Wisconsin constitutes one of the more valuable portions of the reports. The author accepts the general conclusions concern- ing the manner of deposition reached by Whitney some yeai-s since, but works out the

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