280 



INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



At the first-mentioned exposure there is at the base of the Hamilton 28 feet of yeUowish- 

 blue shale, which contains Leiorhynchus limitare. Both the character of the sediment and the 

 fossils remind [one] decidedly of the MarceUus shale of New York. This shale rests unconform- 

 ably (erosional) upon the basal sandstone member of the Onondaga. It is succeeded by a few 

 feet of limestone, which in places is much leached and very fossiliferous, Athyris spiriferoides, 

 Delthyris sculptilis, Rhipidomella penelope, Spirifer granulosus, and StropJieodonta coneava being 

 very common. At points farther north the lower beds of the Hamilton consist of dark-colored 

 impure limestone which succeeds the Onondaga without any apparent break. The character- 

 istic fossils of these layers are Microcyclus discus, Athyris vittata, Eunella attenuata, Spirifer 

 fornacula, Conocardium cuneus, and Onychodus sigmoides. 



The middle portion of the Hamilton limestone is dark colored and evenly bedded and 

 contains Amhocoelia urribonata, Chonetes yandeUanus, C. pusillus, Cransena romingeri, Parazyga 

 Jiirsuta, Pholidops oblata, and Spirifer pennatus. Above this horizon occurs about 25 feet of 

 yellowish-brown impure siliceous limestone with few fossils. Near the top of the formation 

 come in a few feet of hard gray limestone containing OJionetes coronatus, RJiipidomella vanuxemi, 

 Spirifer audaculus, S. pennatus, Tropidoleptus carinatus, and Vitulina pustulosa. 



During Upper Devonian time the Mississippian sea continued to expand, spreading the 

 materials of this formation more widely than the preceding. In the NE. | sec. 34, T. 11 S., 

 R. 2 W., the lower deposits of the Upper Devonian are conformable upon the Hamiltoii. There 

 is here exposed a thickness of 33 feet of yeUowish-brown (black where unweathered) siliceous 

 shale or shaly limestone, cherty near the top, and marked by Leiorhynchus glohuliformis, L. 

 mesacostalis, Reticularia Isevis, and Spirifer pennatus. At other points the upper cherty phase 

 is succeeded by 50 or more feet of greenish to black, almost barren shales. These siliceous 

 and dark-colored shales are probably the equivalent of the "calico rock," a mottled and leached 

 siliceous shale, present farther south in Union and Alexander counties. They doubtless cor- 

 respond with the Chattanooga black shale, Ohio black shale. New Albany black shale, and the 

 Lower Portage beds of other States. 



Generalized section of the pre- Mississippian strata in southwestern Illinois. 



Sys- 

 tem. 



p. 

 P 



■o 



T3 



s 



® 



Correlations. 



New Albany black 

 3 li a 1 e= Chatta- 

 nooga black shale 

 =Ohio black 

 shale=Lower 

 Portage, 86 feet. 



Hamilton, 70 feet. 



Location of sections. 



NE. i sec. 34, T. 11 

 S., R. 2 W., and 

 SE.isec. 1,T. 13 

 S., R. 2 W. 



Descriptions of horizons. 



NE. i^sec.34, T. 11 

 S.,R.2W.,Union 

 County. Section 

 at Back Bone near 

 Grand Tower. 



Marcellus, 28 feet. 



N. i sec. 34, T. 13 

 S.,R. 2 W.Union 

 County. 



Feet. 



Greenish-blue shale, fossils almost none 29 



Black shale with few fossils, but carrying numerous 

 very small balls of iron pyrite from J to J inch in 



diameter 21 



Brown to black, siliceous shale or shaly limestone 

 with Leiorhynchus globuKformis and Reticularia 

 Isevis 36^ 



Light-^y siliceous limestone, in part oolitic, char- 

 acterized by Chonetes coronatus, Cransena romin- 

 geri, Spirifer pennatus, 8. audaculus, Tropidoleptus 

 carinatus, and Vitulina pustulosa 7 



Yellowish-brown siliceous or shaly limestone with 

 few fossils 25 



In the north are dark-colored, fine-grained limestones 

 with Microcyclus discus, Chonetes yandellanus, 

 Eunella attenuata, Parazyga hirsuta, Spirifer for- 

 nacula, and 8. pennatus. In the south are gray or 

 leached limestones with Athyris spiriferoides, Del- 

 thyris sculptilis, Spirifer granulosus, Rhipidomella 

 penelope 38 



Rather soft shale weathering to a yellowish-brown 

 color, with Leiorhynchus limitare .^ 28 



This horizon is not present at the north, in Jackson 

 County. 



