518 GEOLOGY. 



Climate. 



Most of the data at hand indicate that the climate of the Lower 

 Carboniferous was essentially uniform, and on the whole both genial 

 and moist. The fossil plants and corals of so northerly a land as Spitz- 

 bergen, and the relations of the fossils of arctic regions to those of 

 lower latitudes, seem clearly to indicate that climatic conditions were 

 essentially uniform in regions where they are now very diverse. 



The data which seem to be in discord with the conclusion that 

 the climate of the period was genial, moist, and measurably uniform 

 are (1) the salt and gypsum deposits of the Mississippian series in 

 Montana, Michigan and Nova Scotia, and the similar deposits in 

 western Australia, all of which suggest aridity, and (2) certain con- 

 glomerate formations (the Culm) of western Europe. 1 The latter 

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

 seem to warrant this conclusion. The testimony of the marine fos- 

 sils continues to indicate rather uniform and genial conditions. This 

 subject will be touched on again, in the more general discussion which 

 follows. 



THE LIFE OF THE MISSISSIPPIAN (SUBCARBONIFEROUS). 

 I. The Marine Faunas. 



Just as there was no profound break in the stratigraphic progress 

 of the American continent at the close of the Devonian, so there was 

 no radical break in the succession of life. The Devonian fauna passed 

 by gradation into the Mississippian. It will be recalled that the life 

 history of the Devonian in North America consisted of a series of great 

 invasions from different quarters, and that the invaders and the invaded 

 mingled with one another until at the close there was a notable approach 

 to a single continental fauna. This change, however, was not complete. 

 The life of the Great Basin was still largely isolated, and there were 

 dependencies of the main fauna that still retained provincial features. 



During the opening stages of the Mississippian period there was 

 a continuation of the movement from provincialism toward cosmo- 



1 Kalkowsky, Ueber Geroll-Thonschiefer glacialen Ursprungs im Kulm des Franken- 

 waldes. Zeitschr. der deutschen geologischen Gesellschaft, 1893, pp. 69-86. 



