T. E. Savage — Stratigraphy of Southwestern Illinois. 433 



and 2b of the general section described at the end of this 

 article. The lower one (2a) is a sandstone or sandy shale — 

 " Thebes sandstone and shale " — which is exposed along the 

 flanks of .the Thebes and Gale anticlines, and in the interven- 

 ing trough. The materials are reddish-brown where weathered, 

 and blue where not changed by the atmosphere. The lower 

 part is a sandstone, thick bedded and in regular layers, which 

 are well exposed at the east end of the railroad bridge at 

 Thebes. In the upper half the layers are thinner and, where 

 much weathered, appear decidedly argillaceous. This more 

 shaly horizon is weJl exposed in the river bank three-fourths 

 of a mile south of Gale. Lingula cf. covingtonensis occurs 

 sparingly throughout the sandy shale of this member. 



The upper member is a bed of fossiliferous, bluish, shale 

 (2b of the section). It is exposed in the bank of the river, 

 and in a cut along the Illinois Central railway about three- 

 fourths of a mile south of Gale, where it overlies the " Thebes 

 sandstone and shale " member. The bed has a thickness of 

 18 feet, and contains Cyclocystoides n. sp., Phylloporina near 

 granistriata, Dalmanella testudinaria, Plectambonites sericea, 

 Rhynchotrema inmquivalve f , Strophomena sulcata?, Zygo- 

 spira recurvirostra, Conradelia near fimbriata, and species of 

 Isotelus resembling I. susce and /. platycephalus. The litho- 

 logic and faunal change from the Thebes sandstone member 

 to this blue shale is abrupt, which may indicate a break between 

 the two beds. The fauna reminds one much of the Black 

 River formation, but as it occurs in, or immediately above, 

 the Maquoketa series, and its life assemblage is not at all that 

 of the overlying Cape Girardeau limestone, it seemed best to 

 group it with the Thebes sandstone. 



Neither of these members contain Rhynchotrema capax, 

 the widely distributed guide fossil to the Richmond. Indeed, 

 none of their fossils which have yet been determined are deci- 

 sive markers, but the lithology and position of the beds, and 

 their relation to known formations to the north and south, 

 leads to their provisional reference to the Richmond until the 

 complete study of the fauna and the wider study of their field 

 relations shall determine definitely their stratigraphical position. 



The above shales and sandstone do not extend so far north 

 as does the underlying limestone. The sea in which they were 

 deposited probably washed the shores of the Ozarkian land 

 area a few miles to the west, which, during late Richmond 

 time, was the source of the sediments that make up these terri- 

 genous beds. 



Middle /Silurian. 



Alexandrian. — The beds referred to this formation are 

 exposed in Alexander county to a thickness of 44 feet. They 



