SUMMARY OF PALEOZOIC HISTORY 197 



salt-like, lagoon, and marine conditions prevailed in the south- 

 eastern United States. 



Through the era the emergences and submergences of great 

 areas affected the western part of the continent less than the 

 eastern, as proved by the fact that the strata there show fewer 

 unconformities and are rich in limestone, thus indicating greater 

 persistence of oceanic conditions, especially from the Ordovician 

 to the Mississippian inclusive. Of all the west, the Great Basin 

 region appears to have been the most continuously submerged. 



Mountain Making. — During the era there were only two times 

 of great orogenic movements in North America when thick masses 

 of strata were subjected to lateral compression and upraised into 

 mountain ranges. The first of these was toward the close of the 

 Ordovician when the Taconic Mountain range was formed along 

 the eastern border of the continent just east of the present site of 

 the Appalachians. The second was toward the close of the era 

 (Permian) when one of the greatest post-Algonkian physical dis- 

 turbances in the history of North America resulted in the formation 

 of the Appalachian Mountains by folding and faulting of the strata. 



Vulcanism. — The long Paleozoic era was remarkably free from 

 igneous activity in North America, the only extensive intrusions 

 and extrusions of igneous rocks having taken place during the 

 Mississippian (and probably Pennsylvanian) in the northern 

 Cordillera. Some intrusions occurred in eastern Canada during 

 Silurian and probably Devonian time. Other intrusions, usually 

 regarded as of Carboniferous age (either Mississippian or Pennsyl- 

 vanian), occurred in Massachusetts. 



In Europe, however, igneous activity was more frequent and 

 widespread during the era. 



Climate 



The strongest evidence from the character and distribution of 

 the organisms points to a temperate and pretty uniform climate for 

 most part over the globe during Paleozoic time. 



Typical glacial deposits show that extensive areas were glaci- 

 ated about the beginning of the early Cambrian and again toward 

 the close of the era (Permian) . 



Certain deposits such as the "Red Beds," salt, and gypsum 

 indicate at least local arid climate conditions, as for example in 



