DEVONIi^. 279 



The discussion by Savage ''"^^ is in part as follows : 



The rocks of Helderbergian age in Illinois correspond with 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. 



* ** * * * * * * 



The New Scotland formation in Union and Jackson counties has an aggregate thickness 

 of more than 160 feet. The lower portion, for a thickness of 100 feet, consists of shaly limestone 

 with iaterbedded bands of chert. * * * j^ ^i^q cut made by the Frisco Railroad Co. a 

 short distance south and west of Tower Rock 10 species were collected. * * * 



The upper 58 feet of the New Scotland formation is composed of light-gray, heavy-bedded, 

 coarsely crystalline limestone. * * * The beds furnished 17 species. 



The Clear Creek formation consists of light-gray to yellowish colored cherts that are usually 

 in thin layers, but which in the lower part are sometimes 3 to 5 feet iu thickness. * * * 



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 

 Tennessee. The beds represent deposits of the Upper Oriskany time, as is indicated by the 

 iaterwedging of the upper chert layers with those of the basal portion of the succeeding Onon- 

 daga. The chert formation has a thickness, in Illinois, of about 327 feet. Fossils are some- 

 what rare in the lower portion, but in the middle and especially in the upper portion there is a 

 rich fauna." * * * 



The sedimentation of the Upper Oriskany time continued without a break into the Onon- 

 daga or Comiferous. The latter period was initiated by disturbances to the westward, in 

 Ozarkia, which increased mechanical sedimentation in the Illinois area. These resulted for a 

 time in the deposition, along the eastern shore of Ozarkia, of layers of sand containing Onondaga 

 fossils alternating with the return of the Oriskanian limestone conditions. Eventually sand 

 deposition prevailed and there was spread over the basin the basal sandstone of the Onondaga 

 formation, containing [10 species]. 



Early in the Onondaga time an elevation in the southern portion of Union and in Alexander 

 County put a stop to further deposition in these regions, while farther north, in Jackson County, 

 sedimentation was uninterrupted. 



At the cut through the Back Bone and at the Bake Oven, a short distance north of Grand 

 Tower, there is exposed a continuous section of the Onondaga formation showing a thickness 

 of 115 feet. The beds consist largely of Ught-colored, regularly bedded, more or less crystalline 

 limestone, which becomes arenaceous in the lower part. Fossils are abundant throughout the 

 section." * * * 



During the Onondaga and the succeeding Hamilton time the warm waters from the Gulf 

 region, with their successive faunas, spread toward the northeast across Illinois and Indiana, 

 passing around the north end of the Cincinnati axis, and mingled with those of the eastern 

 embayment in western New York. Such water connections permitted continued migrations 

 within this sea and account for the close correspondence between the various Middle Devonian 

 faunas of southwestern Illinois and those of western Ontario and New York. 



Throughout Hamilton time the Kankakee barrier, or peninsula, extending from Ozarkia 

 toward the northeast 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 toward the 

 northwest. 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 southwest Illinois belongs to the New York province. 



The New York faunal phase of the Hamilton is well developed in the south part of Union 

 County, in the N. i sec. 34, T. 13 S., R. 2 W.; and farther north in the NE. i sec. 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. 



a For list of fossils see the work cited. — B. W. 



