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



occupied parts of New York, Maryland, and northeastern Ten- 

 nessee ; and it is probable that the Kankakee barrier, as defined 

 by Schnchert, prevented its spreading far to the north and 

 northwest. 



The New Scotland formation in Union and Jackson comities 

 has an aggregate thickness of more than 160 feet. The 

 lower portion, for a thickness of 100 feet, consists of shaly 

 limestone with interbedded bands of chert. This phase is 

 exposed in the lower part of Bald Rock, four miles southeast 

 of Grand Tower, on the Big Muddy river. It appears in the 

 east bluff of the Mississippi river for some distance south from 

 this point. It makes up Tower Rock, in the Mississippi river 

 channel, west of Grand Tower ; and it is exposed in the quarry, 

 and in the cut made by the Frisco Railroad company a short 

 distance south and west of this rock. At the latter point were 

 collected Streptelasma recta, Dalmanella siibcarinata, Leptwna 

 rhomboidcdis, Leptamisca adnascens, Meristella Iwvis, Spirifer 

 cyclopterus, S. perlamellosus, Stropheodonta ' punctulifera, 

 Hausmannia sp., and Phacops logani var. 



The upper 58 feet of the New Scotland formation is com- 

 posed of light gray, heavy bedded, coarsely crystalline lime- 

 stone. This facies is exposed in the south end of the Back 

 Bone ridge where a fault brings it above the level of the flood- 

 plain. It forms the upper part of Bald Rock, where another 

 fault has raised it to the level of the adjacent Chester lime- 

 stone, of Mississippian a^e. It occurs in the east bank of 

 Clear creek, in sections 23 and 24, T. US., R. 3 W. The beds 

 furnished Aspidocrinus scutellaiformis, Anoplotheca concava, 

 Eatonia singularis, Leptcenisca eoncava, Megalanteris con- 

 doni, Meristella arcuaia f Oriskania sinuata n. var., Spirifer 

 concinnus, S. cyclopterus, S. macropleura, S. perlamellosus, 

 Stropheodonta heckii, S. varistriata, and variety arata, Stro- 

 phonella punctulifera, Uncinulus nobilis f and U. micleolata. 



Oriskanian. — Clear Greek cherts, Camden cherts. — The 

 Clear Creek formation consists of light grey to yellowish 

 colored cherts that are usually in thin layers, but which in the 

 lower part are sometimes three to five feet in thickness. At 

 some points the cherts are thoroughly leached and decom- 

 posed, and occur as a fine white powder that can be dug with 

 a shovel, and is utilized for commercial purposes. 



This formation rests, with erosional unconformity, upon the 

 New Scotland beds at the south end of the Back Bone ridge. 

 It corresponds in age to the Camden cherts of western Tennes- 

 see. The beds represent deposits of the Upper Oriskany time, 

 as is indicated by the inter wedging of the upper chert layers 

 with those of the basal portion of the succeeding Onondaga 

 (see 6a to 6e of section). The chert formation has a thickness, 



