432 MISSISSIPPIAN PERIOD 



The Lower Carboniferous of some parts of Great Britain and 

 western Europe contains much volcanic rock. Some of the erup- 

 tions were probably submarine, and some subaerial. 



The close of the early Carboniferous period was marked, in 

 Europe, by widespread withdrawal of the sea from the area of the 

 continent which it had covered. There were also some mountain- 

 forming movements (folding), as in the Vosges Mountains, in east- 

 ern France, and elsewhere. The development of the Ural Moun- 

 tains appears to have begun at about the same time. These changes 

 shifted the areas of sedimentation notably. 



In other continents, where geological work is less advanced, the 

 Lower and Upper Carboniferous have not always been separated 

 carefully, but the lower system exists in all of them. 



Climate and Duration 



Most of the data at hand indicate the absence of great diversity 

 of climate during the period, and suggest that it was genial. The 

 salt and gypsum in Montana, Michigan, Nova Scotia, and western 

 Australia, imply aridity, but it is not clear that aridity was general. 

 Certain conglomerate formations (in the Culm) of western Europe 

 have been thought to indicate glaciation, but the evidence does not 

 seem to warrant this conclusion. Recently, phenomena which have 

 been interpreted to imply floating ice have been reported from 

 Oklahoma. 1 The duration of the period probably was not less than 

 the average duration of the Paleozoic periods. 



LIFE 



Marine faunas. Just as there was no great stratigraphic break 

 between the Devonian and Mississippian systems in the American 

 continent, so there was no radical break in the succession of life. 



Conspicuous elements of the Kinderhook fauna were (i) the 

 beginnings of the great deployment of the crinoids, which reached 

 their climax later in the period; (2) brachiopods, which were transi- 

 tional between Devonian and Later Mississippian types, the genus 

 Productus being conspicuous (Fig. 377, d. e.}\ and (3) abundant mol- 

 lusks, pelecypods (i, j, Fig. 377) being most numerous. Trilobites 

 were few and small. Their high stage of ornamentation had passed, 

 and the day of their disappearance was drawing near. Fishes, 

 especially sharks, were abundant. 



1 Taff. Bull. Geol. Soc. Am. Vol. xx. p. 701. 



