Wisconsin. Chief Geologist / Geology of Wisconsin. Survey of 1873-1879 ...
Volume I (1883)
Chapter IV. Laurentian age, pp. -79 PDF (8.1 MB)
ARCIATAN (EOZOIC) ERA. CHAPTER IV. LAURENTIAN AGE. FIG. 1. GENERAL SECTION OF THE FORMATIONS OF WISCONSIN. The inclination of the unflexed beds is exaggerated. L. Laurentian. H. Huronian. P. Potsdam sandstone. L. Mg. Lower Magnesian limestone. St. P. St. Peters sandstone. T. Trenton limestone. G. Galena limestone. H. R. Hudson River (Cincinnati) shales. N. Niagara limestone. Hr. Lower Helderberg limestone. Hm. Hamilton limestone (cement rock). Synoptical Notes on Laurentian Formation. Name derived from Laurentide Hills of Canada. Rocks of metamorphic class, mainly gneisses. Thickness un- determined, but great. Strata much folded and contorted. Occupies a large area in Northern Wisconsin. For details see Vol. II, pp. 248-9 (Chamberlin), 461-501 (Irving); Vol. III, pp. 5-6, 92-99 (Irving), 224 (Julien), 248-50 and 300 (Wright), 399-400 (Strong), 434 and 661 (Brooks); Vol. IV, p. 109 (Wooster), 585-601 (King), 617-715 (Irving). Iocation of Early WIsconsin -land. That part of the earliest known formation which falls under our special study formed an island, or group of closely associated islands, lying immediately south of the present Lake Superior, and occupied portions of North- ern Wisconsin and the upper peninsula of Michigan.' General Character of the Rocks. We have already referred to this as the granitic foundation upon which the rock structure of our State is builded. The rocks, as we now find them, consist of a series of granites (quafel-mJ), gneisses (foliatedlfel~-mi-qua), syenites (fel- qua-horn), hornblendic, micaceous and chloritic schists, and allied rocks. With these are associated igneous diabases (plagi-auq), and similar rocks, together with diorites (plag-1-horn) of undetermined origin. Among these rocks, the gneissoid granites vastly predomi- nate, so that the whole series in a general view is conveniently termed granitic. I It is not improbable that this was at one stage united with the adjacent main- land on the west and north.
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