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



Meristella rostrata, RhyncKoneUa gainesi, Spirifer acwmin- 

 atus, S. grieri, S. macra, Stropheodonta pater soni, Conocar- 

 dium trigonale and Onychodus sigmoides. In the lower part 

 Nucleocrinus ver?ieuili, Coscinium cribriformis, Centronella 

 glansfagea, Leptwna rhomboidalis, Meristella harrisi, Penta- 

 merella arata, Spirifer acuminatus, S. duodenarius, S. 

 onacrothyris, Stropheodonta patersoni, Dalmanites calypso, 

 Odontocephalus cegeria and Onychodus sigmoides are common. 



During the Onondaga and the succeeding Hamilton time 

 the warm waters from the Gulf region, with their successive 

 faunas, spread towards the northeast across Illinois and Indi- 

 ana, passing around the north end of the Cincinnati axis, and 

 mingled with those of the eastern embay ment in western New 

 York. Such water connections permitted continued migra- 

 tions within this sea, and accounts for the close correspondence 

 between the various Middle Devonian faunas of southwestern 

 Illinois and those of western Ontario and New York. 



Hamilton. — Throughout Hamilton time the Kankakee bar- 

 rier, or peninsula, extending from Ozarkia towards the north- 

 east across Illinois, was largely effective in preventing the 

 waters of the Interior or Mississippian sea from uniting with 

 those of the Northwestern or Dakotan basin towards the north- 

 west. As a result of this separation the deposits and the 

 faunas of Hamilton time, in Illinois, belong to two distinct 

 provinces. The phase of the Hamilton in the vicinity of 

 Rock Island, and in Jersey and Calhoun counties, belongs to 

 the Northwestern or Dakotan province ; while that of south- 

 west Illinois belongs to the New York province. 



The New York fajmal phase of the Hamilton is well 

 developed in the south part of Union county, in the north 

 half of sect. 34, T. 13 S., R. 2 W. ; and further north in the 

 N.E. \ of sect. 34, T. 11 S., R. 2 W. The formation is also 

 represented in the upper beds near the north end of Back 

 Bone ridge, in Jackson county. 



At the first mentioned exposure there is at the base of the 

 Hamilton 28 feet of yellowish-blue shale, which contains 

 Leiorhynchus limitare. Both the character of the sediment 

 and the fossils remind decidedly of the Marcellus shale of 

 New York. This shale rests unconformably (erosional) upon 

 the basal sandstone member (7a) of the Onondaga. It is suc- 

 ceeded by a few feet of limestone which, in places, is much 

 leached and very fossiliferous ; Athyris spiriferoides, Del- 

 thyris sculptilis, Rhipidomella penelope, Spirifer granulosus 

 and Stropheodonta concava being very common. At points 

 further north the lower beds of the Hamilton consist of dark 

 colored, impure limestone which succeeds the Onondaga with- 

 out any apparent break. The characteristic fossils of these 

 layers are Microcyclus discus, Athyris vittata, Eunella atten- 



