70 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 76 



more or less widely spaced invasions of but slightly modified stages 

 in the evolution of the life history of a particular marine breeding 

 ground alternating in the same sections with similarly related emana- 

 tions from another source might be cited. However, those men- 

 tioned sufficiently illustrate the general idea I am intending to convey. 

 Besides, some of them — like the notable cases of the Utica and the 

 Maquoketa that concern grajDtolites and other thin-shelled remains 

 usually found in Ordovician and Silurian deposits of black shale — 

 require too much explaining. Therefore, all I think worth adding 

 is that in all the mentioned cases the alternating changes in the char- 

 acter of the faunas are never complete. Evidently the invasions 

 from the farther source in passing through some part of the nearer 

 source joined the usually smaller contribution of the latter. Then, 

 when the supply from the more distant source was reduced or com- 

 pletely cut off some of its species that had gained a foothold in the 

 nearer source were thus included in its subsequent contributions. It 

 is to be noted further that when these changes occurred the ensuing 

 invasion usually included also a few and sometimes many contri- 

 butions from other previously excluded sources; and it is these en- 

 tirely new migrants that constitute the most reliable and the most 

 easily notable of its guide fossils. 



Progress in middle western and Gordillercm regions. — Extremely 

 interesting and important stratigraphic results have developed in 

 the course of field and laboratory investigations of the character 

 and geographic distribution of faunas and formations in Oklahoma. 

 These relate particularly to demonstrations of early and middle 

 Paleozoic surface undulations and consequent shiftings of the 

 strandline on the flanks of the Arbuckle and Wichita uplifts in the 

 south central part of the State. Comparison of numerous cross- 

 sections shows that the sequence of formations on their flanks varies 

 greatly and rapidl}^ from place to place. And the faunal evidence, 

 doing its part in the elucidation of the geological history of North 

 America, shows that these areas suffered alternating invasions from 

 the Pacific, Arctic, Atlantic, and southern sides of the continent 

 during each of the Cambrian, Ozarkian, and Ordovician periods. 

 Much of the doubt and misapprehension that has prevailed in Okla- 

 homa stratigraphy, especially as regards relations to deposits in 

 the adjoining States of Missouri and Arkansas, is being explained 

 in orderly fashion by these discoveries. Each of the pre-Mississip • 

 pian formations of preceding classifications is being divided on 

 faunal and diastrophic criteria into two to six clearly distinguishable 

 formations; and the locally extremely varying great sequence of 

 limestone deposits that in Taff's classification is called Arbuckle 

 limestone is split up into one Cambrian, six Ozarkian, and three 



