T. E. Savage — Stratigraphy of Southwestern Illinois. 435 



Silurian. 



Clinton. — The limestone of this formation has here a max- 

 imum thickness of 75 feet. One-half mile southeast of Gale 

 it immediately overlies the " Thebes sandstone and shale " ; 

 the shale member (25 of section) and all of the Alexandrian 

 beds having been cut out by erosion prior to the deposition of 

 the Clinton. One and one-half miles north of Thebes the 

 Clinton limestone rests on the Whitfieldella hillingsana mem- 

 ber (3e of section), while two miles south of Thebes it imme- 

 diately overlies the Cape Girardeau limestone (Sa of section). 

 The upper part of the Clinton (4c) consists of heavy bedded, 

 pink or mottled limestone, 23 feet thick, which contains many 

 small, immature brachiopods, besides Pleetambonites transver- 

 salis, Rafinesquina mesacosta, Spirifer near sulcata, Illcemcs 

 sp., and a few new species of Orthoceras. Below this pink 

 limestone lie 6 feet of thin-bedded, dark gray limestone with 

 narrow bands of chert (45 of section). The limestone layers 

 contain Favosites favosus, Halysites catenulatus, Stromato- 

 pora sp., Atrypa rugosa, Orthis cf. davidsoni, Orthis Jlabel- 

 lites, Pleetambonites transner sails, and var. elegantula, Striek- 

 landinia triplesiana and Triplecia oi'toni. The above fauna 

 corresponds with that of the Interior or Western Clinton, as 

 described by Foerste from the region of Dayton, Ohio. 



The lower portion of this formation (4a) is well ex|)osed in 

 the vicinity of Gale, and two miles further north, along Sexton 

 Creek in the N.W. \ sect. 27, T. 14 S., K. 3 W., where it con- 

 sists of 46 feet of thin-bedded, gray limestone, the layers of 

 which are separated by narrow chert bands. 



The thickness of the Clinton is variable. It does not exceed 

 29 feet in the exposure south of Thebes, while near Gale and 

 along Sexton creek and in the river bluff two miles east of 

 McClure the aggregate thickness is 75 feet. Where the for- 

 mation is thinnest it is the lower and not the upper layers that 

 are absent. 



Devonian. 



Helderbergian. — The rocks of Helderbergian age in Illinois 

 correspond w T ith the New Scotland formation of New York. 

 They succeed the Clinton after an exceedingly long land interval, 

 represented by all of the Silurian after the Clinton, and the 

 Coeymans of the Lower Devonian. In New Scotland time the 

 Interior or Mississippian sea was much more restricted than 

 during the Clinton. According to an unpublished paleogeo- 

 graphic map of the time, by Schuchert. this sea extended as an 

 embay men t from the Gulf region as far north as Jackson 

 county, Illinois. It spread west to Indian Territory and east 

 as far as southeast Tennessee. It was separated by a land bar- 

 rier from the Atlantic embayment (Cumberland basin) which 



