May 22, 1885.] 



SCIENCE. 



429 



reasons. The science of geology has received 

 no insignificant contribution in these publica- 

 tions. Much light has been thrown upon 

 some unsettled problems ; and 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, 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 intervals 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 Huronian series. 

 The rocks 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 

 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 

 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 upon 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 remains room for doubt. In any 

 event, the important fact developed is the exist- 



ence of a distinct formation 3'ounger than the 

 Huronian, and unconformable 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 quaternar} T geolog} r , Wiscon- 

 sin is an exceptionally good field, because of the 

 proximity of driftless, old-drift, and new-drift 

 areas. The determination in 1874, of the 

 morainic character of the previously 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 valle3 T . 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 since 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 recognition of two clearly 

 differentiated ice-epochs 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 slightly 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 hy 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 



