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Geology of Wisconsin

By I.A. Lapham

A large portion of the northern part of this state is underlaid by Granitic Metamporphic, and Trap rocks, which have received but little examination by geologists. They were formerly called primative, and azoic rocks, names which would still be applicable here, for there are proofs of their great age, and they have not yielded traces of animal or vegetable remains. They consist of granite, syenite, gneiss, mica-slate, hornblende rocks, argillite, quartzite, iron ores (both specular and magnetic), ferriferous, and chloretic slates &c. Among them may be found the Laurentian & Huronian rocks of the Canadian geologists, but their characters are too little known to admit of certainty in regard to their age & parallelism with rocks of other states. They are very variable in their composition seldom presenting the same color or appearance for any considerable distance.