Page:Science vol. 5.djvu/463

 Hat 91, 1885.1

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��reasons. The science of geolc^j' has received no insignificant contribution in tticse publica- tions. Much light has been thrown upon some unsettled problems ; Rnd if they are still unsettled, or if their solutions are still disputed, the contribution is not less real, because the data afforded by the state are insufficient bases for positive conclusions. Each formation of the state has been carefully mapped ; its strati- graphical relations determined : and its fossils, when fossils exist, identiBed. Ninety-four new species are described and figured, as also are some of the more characteristic forms pre- viously known.

Among the more imjxtrtant and interesting results are the determinations which have been made respecting the subdivisions of the archaeaa 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 intenals which, in jKiiut of time, were of DO inconsiderable duration, — intervals long enough in each case to allow profound changes, both stratigraphical and petrc^raphical, 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 ta occur between the Laurentian and lluronian series. The rocks of the Lanreutian series are much more highly metamorphosed than those of the Huronian which overlie them ; they are in a highly folded and contorted state, white the Huronian rocks have suffered notably less stratigraphical distortion : the laminations of the two series, when seen in contact or prox- imity, are discordant; the later series con- tains, at its very base, material from the older bjghlj' 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 upon which the subtU- 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, aud from the Potsdam on the other, rests on scarcely less l)ositive grounds. The question as to whether the Keweenawan group is to be classed as Cambrian or pre-Cambrian, is one concerning which there remains room for doubt. In any event, the important fact developed is the exist-

��ence of a distinct formation younger than the Huronian. and uncoufonnably subjacent 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 geologj', Wiscon- sin is an exceptionally good field, because of the proximity of driftless, old-drift, and new-drift areas. The determination in 1((74, of the morainic character of the preiiously known ' Kettle Range ' of eastern Wisconsin, gave 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 and principles here first developed have been the key to the explanation of glacial phenomena siuce studied from the Atlantic to Dakota. The determination of hitherto unsuspected moraines, and the connection of these with each other and with moraines pre- viously known, but not known to have more than local developments, quickly followed in the wake of the first determinations in Wis- consin. Another result, scarcely less sig- nificant, was the reci^nition of two clearly differentiated ice-epochs in the glacial period, separated, according to Professor Chamborlin, 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 slightly modified the borders of the driftless area as mapjied 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 Moraine, which marks the limit of ice advanced in the second epoch, as interpreted by Professor Chamberlin, there is an area covered with glacial drift, which, as indicated by the greater amount of erosion which it has suffered, is of much less recent origin than that within the Kettle Moraine.

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 years since, but works out the

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