ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 500 



PENNSYLVANIAN 



Text fig. 2 - Geologic interpretation of cross section through the Spencer 

 Farm locality. 



dolostone. The early Pennsylvania]! deposits were, as they are today, 

 located between fairly steep bluffs of the St. Louis and Salem Limestones 

 (text fig. 2). The geology of this locality has been described by Leary 

 (I97^a). 



The geologic position of the flora-bearing beds is not directly 

 obvious in the field because much of the area is covered and the Penn- 

 sylvanian as well as Mississippian strata are essentially flat lying. 

 The first impression in the field is, therefore, that the plant-bearing 

 beds are overlain by the Salem and St. Louis Limestones. The flora and 

 the irregular predepositional surface, however, are clear indications 

 of the Pennsylvanian age of the plant-bearing beds. 



Caves , sinkholes , and channels containing Pennsylvanian age shale 

 and sandstone are present in Ordovician, Silurian, and Devonian lime- 

 stones in Rock Island (Savage and Udden, 1921), Whiteside (McGinnis and 

 Heigold, 191k), La Salle (Willman, 19^2), and Kankakee (Bretz, 19^0) 

 Counties. Plant megafossils have been found in deposits in Rock Island 

 County since the last century (Worthen and Shaw, 1873). Caves containing 

 Pennsylvanian age material are known from Missouri; Upshaw and Creath 

 (1965) described a spore flora of early Pennsylvanian age from these de- 

 posits. Brill (1973) reported a linear deposit bearing fragmentary Penn- 

 sylvanian plant fossils in St. Louis County, Missouri, and he interpreted 

 it as a fossil valley. 



Leckwijck, Stockmans , and Williere (1955) described a locality 

 in Belgium that shows many similarities to the Spencer Farm site. In 

 that locality Namurian shales, which were deposited in solution cavities 

 in Vis£an limestone, preserved an unusual flora that is known from only 

 a few other places. 



Stratigraphy 



A composite stratigraphic section of the deposits in the vicinity 

 of the fossil locality is shown in text figure 3. Information on local 



