ORDOVICIAN-CAMBRIAN BOUNDARY 653 



Page Plate 



Ordovician, Varying stages of 339 



Ordovician-Cambrian boundary 585 



Relations of 294 



Ordovician-Silurian boundary 585 



Ordovician (late) Silurian (early) period of diastropbic activity. 468 



Oregon dolomite 520 



Organic evolution 497 



remains. Use in correlation of 506 



Origin and dispersal of fossil marine faunas 483 



Oriskany group . . 28 



limestone 528 



sandstone 528 



Orogenic movements 407, 436 



Orr formation 612 



Orthis electra 671 



Orthoceras 639 



cf . primogenium 671 



Orthorbyncula linneyi 509, 514 



Ortbothetes subplanus 577 



Orusia lenticularis 646 



Osage group 427 



Osagian 587 29 



Oscillating seas and lands a basis of new stratigrapbic geology. . . 403 



Oscillations : Adirondack uplift 415 



Causes of differential 430 



Cincinnati geanticline 416 



Mississippi Valley 419 



Niagaran 424 



of level. Diagram illustrating 343 



Paleozoic 304 



post-Ordovician 421 



Rhythmic occurrence of 579 



Silurian 422 



Small vertical range in Paleozoic 335 



Oscillatory character of continental seas 320 



Osgood 28 



limestone (= Rochester shale) 558 



Ostracoda, Distribution of 505 



Oswego formation 473 



in New York and Pennsylvania 311 



sandstone 469. 565, KS7: 



Ottosee bryozoan fauna 557 



formation 453, 563 



shale 538, 539. 7C>7>. 556, 557 



Ouachita geosyncline 476 



shale in Arkansas 676 



synclines 528 



trough 177, 67<; 



XLV--Buix. GBOL. BOC, Am., V«»i, 24, 1012 



