THE CARBONIFEROUS PERIODS 507 



Paleozoic, but if a Mesozoic table were examined it would be found 

 that these inconspicuous forms became prominent in the latter. 



Climate. — Our knowledge of the climate of the Paleozoic is not 

 extensive. As a whole, the evidence points to uniform conditions 

 and no well-marked climatic zones. There were, however, glaciers 

 in certain regions in the Cambrian and Permian, and perhaps in other 

 periods. Certain areas were arid during portions of the Paleozoic, 

 as their red sediments, gypsum, and salt show, the aridity having prob- 

 ably been caused in most regions by elevated land areas which shut 

 off the moist winds of the oceans. 



REFERENCES FOR THE CARBONIFEROUS PERIODS 



Blackwelder and Barrows, — Elements of Geology, pp. 369-396. 



Chamberlin and Salisbury, — Geology, Vol. 2, pp. 496-677. 



Grabau and Shimer, — North American Index Fossils, Vols. 1 and 2. 



Schuchert, Chas., — P 'ale geography of North America: Bull. Geol. Soc. America, 



Vol. 20, 1910, pp. 494-498. 

 Scott, W. B., — An Introduction to Geology, pp. 609-654. 

 Ulrich, E. O., — Revision of the Paleozoic Systems: Bull. Geol. Soc. America, Vol. 22, 



1911. 



