Bulletin of the Geological Society of America . ion 558 References 558 Precambrian Crystallines A glance at the geological map of that part of the United States lyingbetween the Mississippi River and the Rocky Mountains will reveal sixregions of mountain uplift, namely, the Black Hills, the Ozarks, theOuachitas, the Arbuckles, the Wichitas, and the Llano Mountains (some-times called the Central Mineral Region) of Texas. The general struc-ture of all these mountains is essentially the same, being in each case a ^ Manuscript received by the Secretary- of the Society February 7, 1923. (541) 542 C
Bulletin of the Geological Society of America . ion 558 References 558 Precambrian Crystallines A glance at the geological map of that part of the United States lyingbetween the Mississippi River and the Rocky Mountains will reveal sixregions of mountain uplift, namely, the Black Hills, the Ozarks, theOuachitas, the Arbuckles, the Wichitas, and the Llano Mountains (some-times called the Central Mineral Region) of Texas. The general struc-ture of all these mountains is essentially the same, being in each case a ^ Manuscript received by the Secretary- of the Society February 7, 1923. (541) 542 C. X. GOULD CEYSTALLIXE EOCKS OF THE PLAINS truncated dome. Except in the case of the Ouachitas, the sedimentarieshave been removed by erosion over the core of the uplift and the sub-jacent crystalline rocks have been ^sposed (see figure 1). The greater part of the igneous rocks exposed in the cores of thesevarious mountains is Precambrian in age, and the rocks vary consider-ably, both in composition and in texture. In the Black Hills the crys-. ^^ PrE-CamBMAN CRVSTAUUtNE O 4-Post-Cam BRIAN Cr>.3Ta Li-i •• a Figure 1.—Location of Occurrences of Crystalline Rocks on the Plains talline rock is largely gneiss, schist, and granite: in the Ozarks it con-sists chiefly of granite and rhyolite, with intrusive dikes of diabase; inthe Arbuckles the igneous rock is chiefly coarse granite and gray andreddish porphyry; in the Wichitas it is largely red and black granite,gabbro, and porphyry, while in the Llano Mountains the igneous rockconsists largely of schist and gneiss, with intrusions of granite, gabbro,and diabase. TRECAMBRIAN CKYSTALLINES 543 The sedimentaries exposed, dipping quaquaversally along the flanksof these various mountain ranges, vary in age from Cambrian to Ter-tiary. In the Black Hills the sedimentary rocks include Cambrian,Ordovician, Carboniferous, Triassic, Jurassic, and Cretaceous sedi-mentaries; in the Ozarks, Ouachitas, and Arbuckles there are rocks ofeach
Size: 1607px × 1554px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1890
