algae, the diatoms have numerous shapes and structures (discoid, elliptic, 

 rhombic, triangular, etc.). They are found in fresh, brackish, and marine sedi- 

 ments and have a geologic range from the Cretaceous to Recent. Like pelagic 

 foraminifera, diatoms are used sometimes for long-distance correlation. 



Charophyta (PI. 11-1, figs. 12-14) 



The Charophyta or stoneworts are algae believed to be distantly related to 

 the Chlorophyceae. They are composed of erect stems consisting of nodes and 

 internodes. The fossil remains of the Charophyta are formed by an accumula- 

 tion of calcium carbonate about the plant; usually only the female reproductive 

 body, the oogonium, is found fossilized. The oogonia have characteristic spiral 

 ornamentation which make them easily recognizable. Stoneworts with sinistral 

 spiraling are known from the Devonian to Recent and those with dextral spiral- 

 ing from the Lower Devonian to Lower Mississippian. 



Recent Charophyta occur in fresh- and brackish-water environments. How- 

 ever, some workers believe that the earlier forms may have had near-shore and 

 marine habitats. More work is needed on these interesting fossils before they 

 can be used in close correlation work. At the present they are valuable only in 

 determining broad geologic time subdivisions. 



Plant Spores and Pollen 



Plant spores and pollen have become very useful and adaptable in strati- 

 graphic paleontology during the last decade. The present status of these plant 

 microfossils is comparable to that of foraminifera thirty years ago. More and 

 more oil companies, recognizing the stratigraphic importance of these microfos- 

 sils, are adding personnel to their paleontological staffs for the purpose of in- 

 vestigating these fossils. 



Plant spores were observed as early as 1833 by Witham, who described them 

 from bituminous coals in England. Since 1930, workers have used them for the 

 recognition and correlation of coal seams both in this country and abroad. The 

 Illinois State Geological Survey and others have done extensive work using fos- 

 sil spores for correlating Paleozoic coals. 



Unlike the foraminifera, which are confined almost entirely to marine sedi- 

 ments, spores and pollen occur in both marine and non-marine strata. Spores 

 and pollen are widely distributed in a variety of sediments by wind, water, grav- 

 ity, and insects. Foraminifera have different representatives in each type of the 

 different marine environments, such as near shore, offshore, shallow water, and 

 deep water. Therefore correlation across facies boundaries is often difficult. In 

 contrast, the same species of spores and pollen are encountered in rocks laid 

 down in all types of environment, thereby permitting correlation across different 

 depositional facies. 



212 



