154 



HISTORICAL GEOLOGY 



The flora of the period consists almost entirely of the highest 

 Cryptogams (i.e. Pteridophytes) and the simpler Phanerogams 

 (i.e. Gymnosperms) . As in the Devonian, all the principal groups 

 of the Pteridophytes — Lycopods, Equisetce, and Ferns — as well 

 as the still higher Seed-ferns and simpler types of Gymnosperms 

 were represented. All of these plant types are of unusual interest 

 and importance but, because of their vastly greater abundance 



Fig. 90 



Mississippian Cup-corals, Lonsdaleia canadense, forming a compact mass or 

 colony. (After Ulrich, U. S. Geological Survey, Folio 95.) 



and better state of preservation in the Pennsylvanian rocks, it 

 will be best to postpone their somewhat detailed discussion to the 

 next chapter. 



Protozoans. — Foraminifers were exceedingly abundant, es- 

 pecially in the Mid-Mississippian (St. Louis) sea. The famous 

 Bedford limestone of Indiana, for example, is very largely made up 

 of the tiny calcareous shells of these Protozoans. Radiolarian 

 (siliceous) shells are very abundant in some formations where 

 they make up layers of chert. 



