16 Schuchert and Barrett — Revised Geologic 



(1876) from the river of that name in Kansas and Wyoming 

 could take its place in America. 



The geologic time-table. — The time is not yet at hand for a 

 complete evaluation of the minor diastrophic movements, 

 because the recorded geologic succession in the different coun- 

 tries is by no means the same. For instance, the chronology 

 of Africa south of the Sahara desert is in the main one of 

 erosion, with a wonderful record of continental deposits and 

 glacial formations. In other words, this continent throughout 

 time has generally stood well above the pulsating oceans, and 

 owing to reelevation in recent geologic periods now stands at 

 an average elevation of 2000 feet above sea-level. North 

 America, on the other hand, lay near sea-level throughout 

 the Paleozoic, was often in part submerged, and therefore has 

 recorded in its rocks the most complete history of this era ; but 

 during the Mesozoic the greater eastern half of the continent 

 was continually above the sea. The Mesozoic marine sedi- 

 mentary record is in consequence restricted to a narrow strip 

 along the Atlantic, to a wider area along the Griilf and Pacific 

 margins, and to the Great Plains country, over which there 

 flowed great inland seas from Mexico to the Arctic in Cre- 

 taceous time. To find the Mesozoic history in greater perfec- 

 tion we must look to the countries to the north of the Mediter- 

 ranean. On the other hand, the Ordovician period is closed 

 in America by the Taconic disturbance (named from the 

 Taconic mountains of eastern New York), when low mountains 

 were thrown up from Virginia to Newfoundland ; whereas this 

 movement is hardly registered in Europe outside of Great 

 Britain. And again, the Silurian throughout western Europe 

 is closed by the Caledonian disturbance, when mountains were 

 raised from Ireland and Scotland through Norway into arctic 

 Spitzbergen ; while in America no marked elevation then took 

 place. In early and middle Devonian time, however, all north- 

 eastern North America was in the throes of mountain-making 

 and decided volcanic activity ; this is the Shickshock dis- 

 turbance so well seen in the mountains of the same name in 

 southern Quebec and Gaspe. 



Because of these unsatisfactory conditions in our present 

 knowledge of the earth's history, we are not in a position to 

 state that the periods in our table are the only ones that will 

 eventually be recognized in North America. On the contrary, 

 we confidently expect to see evidence developed to show that 

 the Mississippian period embraces two diastrophic cycles or 

 periods (Tennesseian and Waverlian) ; the Ordovician has cer- 

 tainly two and apparently four (Cincinnatian, Champlainian, 

 Canadian and Ozarkian); while the Cambrian has three ( Croix - 

 ian, Acadian, and Waucobian). To keep these movements or 



