Pre-Cambrian Geology of North America

Voorkant
U.S. Government Printing Office, 1909 - 939 pagina's
 

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Pagina 495 - In the third and uppermost horizon, consisting of beds of graphite, occurred great numbers of spicules of apparently hexactinellid sponges. "Between this upper Laurentian system and the basal Cambrian occurs," says Matthew, " a third system, the Coldbrook and Coastal, Huronian, which has given conglomerates to the Cambrian and has a great thickness.
Pagina 117 - Superior, we have the following conclusions : " On the whole, we are disposed to regard the specular and magnetic oxides of iron as a purely igneous product, in some instances poured out, but in others sublimed from the interior of the earth. The supposition entertained by some that...
Pagina 450 - ... follow the outcrop of each important mass in all its windings as far as it can be traced, until it becomes covered by superior strata, is cut off by dislocation, or disappears by thinning out.
Pagina 715 - ... slate — in fact, all possible gradations and mixtures of the minerals dolomite, hematite, quartz, and such argillaceous minerals as kaolin and chlorite. In the ferruginous rocks associated with the iron ore the iron occurs as hematite and also in the form of carbonate, isomorphous with...
Pagina 388 - Part II. Keweenaw Point with particular reference to the felsites and their associated rocks by LL Hubbard.
Pagina 547 - Report on an Exploration in 1875, between James Bay and Lakes Superior and Huron.
Pagina 33 - The fauna includes four species of annelid trails and a variety that appears to have been made by a minute mollusk or crustacean. There also occur in the same shales thousands of fragments of one or more genera of crustaceans.
Pagina 115 - Near lYAnse is a limited patch of limestone which has a dip to the east of 25į to 30į, the limestone being distinctly stratified. The sandstone about a quarter of a mile to the north is horizontal, and it seems evident that the limestone overlies the sandstone, although the position of the inclined beds of the more southerly portion of the limestone is difficult to explain, since the surrounding country is low and level and underlain by sandstone and horizontal beds.
Pagina 738 - Granite is the principal mountain-making rock in the Wichita region. Its area is greater than that of all the other igneous rocks combined, and is about equal to that of the others and the older Paleozoic sediments. It makes all of the high land of the Wichita, Quana, Devils Canyon, and Headquarters mountains, and a large part of the Raggedy group. "The relations of the granite to the gabbro indicate that the granite is younger and that it intrudes the gabbro. Both occur in large masses, as shown,...
Pagina 256 - ... dip, at a high angle usually. But- subsequently a very extensive outburst of granite, with some syenite, has taken place, to the great disturbance of the stratified rocks, and penetrating them both in intercalations and crosswise. These intrusive rocks occupy a very large portion of the lake, most of the western shore, nearly all of the eastern trough or arm.

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