The structure of the rocks is hypocrystalline-porphyritic on account of the occurrence of an isotropic base and the repetition of the crystallization of pyroxene, nepheline and feldspar. Although the specimens by their whole habit and structure belong under the head of nepheline-basanite poor in olivine, the presence of sanidine as phenocrysts causes them to form a transition to the group of phonolites. Unfortunately, analyses of these rocks have not yet been made. A microscopical examination of the basaltic rock from Pilot Knob, near Austin, Travis County, was made for the purpose of comparison with the rocks from southern Texas just described. The rock was found to be a nepheline-basalt porphyritic with numerous phenocrysts of olivine. The fine grained groundmass consists essentially of augite-crystals cemented by non-individualized nepheline in very small amount. A. OSANN. SOME DYNAMIC PHENOMENA SHOWN BY THE BARABOO QUARTZITE RANGES OF CENTRAL WISCONSIN. The quartzite ranges of Baraboo extend east and west for about thirty miles, one lying north, and the other, the main range, lying south of the City of Baraboo. The geology of this district is admirably given by the late Professor Irving.[8] Not only is the general geology clearly described, but remarkably accurate descriptions are given of the character of the quartzite, and the phenomena shown by it, considering the fact that the report was written nearly twenty years since. The unconformity existing between the quartzite and the Cambrian was later more fully described.[9] The induration of the Baraboo quartzite has been explained as due to the enlargement of the original quartz grains; and to the deposition of independent interstitial quartz.[10] The present note is based upon recent observations on the East Bluff at Devil’s Lake and on the exposures at the Upper Narrows of the Baraboo River. The section across the ranges, as given by Irving, is shown by Fig. 1. The two ranges together, as thus represented, are less than the north half of a great anticline, the south side of the south range being near its crown. This structure involves a very great thickness of quartzite, and was offered with reservation by Professor Irving. He says: “The hypothesis is not altogether satisfactory. The entire disappearance of the other side of the great arch, as well as the peculiar ways in which the ranges come together at their extremities are difficult to explain by it. It may be said in this connection that the dip observations toward the west are not so satisfactory or numerous as they might be.” The question naturally arises whether or not the great width of the ranges in the central part of the area may not be partly explained by monoclinal faulting, and thus reduce the supposed thickness of the beds. [Illustration: FIG. 1.--Ideal Sketch, showing structure and amount of erosion of the Baraboo Ranges. After Irving. Scale natural, 12,000 feet to the inch.]