AN EARLY PENNSYLVANIAN FLORA WITH 



MEGALOPTERIS AND NOEGGERATHIALES 



FROM WEST-CENTRAL ILLINOIS 



Richard L. Leary 1 and Hermann W. Pfefferkorn 2 



ABSTRACT 



The Spencer Farm Flora is a compression- impression 

 flora of early Pennsylvanian age (Namurian B, or possibly 

 Namurian C) from Brown County, west-central Illinois. The 

 plant fossils occur in argillaceous siltstones and sand- 

 stones of the Caseyville Formation that were deposited in 

 a ravine eroded in Mississippian carbonate rocks. The 

 plant-bearing beds are the oldest deposits of Pennsylva- 

 nian age yet discovered in Illinois. They were formed be- 

 fore extensive Pennsylvanian coal swamps developed. 



The flora consists of 29 species and a few prob- 

 lematical forms. It represents an unusual biofacies, in 

 which the generally rare genera Megalopteris , Lesleya, 

 Palaeopteridium, and Lacoea are quite common. Noegger- 

 athiales, which are seldom present in roof- shale floras, 

 make up over 20 percent of the specimens. The Spencer Farm 

 Flora is an extrabasinal (= "upland") flora that was grow- 

 ing on the calcareous soils in the vicinity of the ravine 

 in which they were deposited. 



It is suggested here that the Noeggerathiales may 

 belong to the Progymnosperms and that Noeggerathialian 

 cones might be derived from Archaeopteris-like fructifica- 

 tions. The cone genus Lacoea is intermediate between 

 Noeggerathiostrobus and Discinites in its morphology. 



Two new species, Lesleya cheimarosa and Rhodeop- 

 teridium phillipsii , are described, and Gulpenia limbur- 

 gensis is reported from North America for the first time. 



INTRODUCTION 



The Spencer Farm Flora (table l) differs from other Pennsylvanian 

 floras of the Illinois Basin. Many genera and species in the Spencer 

 Farm Flora either have not been found elsewhere in the basin or are very 



•'-Curator of Geology, Illinois State Museum, Springfield. 



2 Formerly of Illinois State Geological Survey; presently at Department of Geology, 

 University of Pennsylvania, Philadelphia. 



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