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limestone of New York. The name Clear Creek formation has 

 been applied to the Devonian beds in Illinois that correspond 

 in age with the upper Oriskany portion of the New York 

 Devonian. 



Distribution and Conditions of Deposition.. The 

 Grand Tower formation, like the lower Devonian strata in 

 Illinois, is thought to have been laid down in a nar- 

 row arm of the sea that had connection southward with 

 the Gulf of Mexico. It is found in our state over only a small 

 area in the extreme southern part. At the base it consists of 

 25 to 30 feet of sandstone, which is succeeded by about 125 

 feet of limestone, making an aggregate thickness for the for- 

 mation of about 155 feet. 



- The sandstone of the Grand Tower formation overlies the 

 Clear Creek, or Upper Oriskany, beds with no intervening 

 break in sedimentation. The quiet conditions under which 

 the Oriskany strata were deposited in this region were broken 

 by a movement to the westward, in Ozarkia, which increased 

 mechanical sedimentation over this portion of the basin. The 

 movement was intermittent, and resulted for a time in the 

 deposition, along the west border of the embayment, of layers 

 of sand containing a mingling of Onondaga and Oriskany 

 fossils, alternating with periods of quiet during which lime- 

 stone layers, containing typical Oriskany fossils, were accumu- 

 lated. As a result, there is in this region an interwedging 

 of the upper layers of the Oriskany and the basal portion of 

 the Grand Tower strata along the zone of contact of these 

 formations. Eventually sand deposition prevailed, and there 

 was spread over the basin a mantle of sand 20 to 30 feet in 

 thickness, which constitutes the lower member of the Grand 

 Tower formation. This sandstone is exposed in the south- 

 west part of Jackson county, and at numerous points further 

 south, in the counties of Union and Alexander. 



After the deposition of the basal sandstone, there was a 

 further movement in the Ozarkian region of Missouri, that 

 resulted in pushing the west shore of the sea further east- 

 ward in southern Union and in Alexander county, and put a 



