12 THE DEVONIAN OF MISSOURI. 



Description. — The Cooper limestone is usually a bluish-gray, 

 compact, very fine-grained rock that resembles the so-called 

 lithographic limestone of northeastern Missouri. In places the 

 lower beds are almost black and are not quite so compact and 

 homogeneous. 



In Pettis, Cooper, Moniteau and Morgan counties the upper 

 2 to 4 feet of the limestone contains cavities filled with calcite 

 which give the rock a mottled appearance. It seems to have 

 been honeycombed with borings like those of the vermicular 

 sandstone and the holes were later filled by deposition from 

 solution. 



In Western Boone and eastern Moniteau counties the rock 

 is all light colored but is much more irregular in both color and 

 texture than that farther west. In Marion and Ralls counties 

 the rock is not as homogeneous and fine-grained as in the out- 

 crops in Pettis and Cooper counties. 



In thickness the Cooper ranges up to 30 feet but is rarely 

 more than 20 feet and averages less than 15 feet. On Clear 

 Creek in Cooper County, Swallow lists 20 feet of Cooper marble, 

 but the writer has not seen thicknesses greater than 16 feet. 

 At Pinhook Bridge, in Pettis County, northeast of Sedalia, 

 about 30 feet of blue limestone above and nearly black limestone 

 below is exposed and the bottom is covered. In a quarry at 

 Sweeney on the Missouri, Kansas and Texas tracks, about 15 

 miles east of Sedalia, the upper part of the Cooper, all light 

 colored, is well exposed. 



Relationships and Distribution. — Outcrops of Cooper lime- 

 stone are known in Pettis, Cooper, Morgan, Moniteau, Saline, 

 Boone, Ralls and Marion counties. Its thickest and most typical 

 exposures are in Cooper and Pettis counties. The thickest 

 section known to the writer is at Pinhook Bridge, northeast of 

 Sedalia in Pettis County. The most extensive exposures are 

 along the Lamine valley below Sweeney in Cooper County. 



The formation is not continuous but represents erosion 

 remnants. In the bluffs of the Missouri River in Boone County 

 it outcrops intermittently for about ten miles ranging up to 15 

 feet in thickness. It was deposited on a greatly eroded surface 

 and was extensively eroded before the Callaway limestone was 

 deposited on it. For distances of a mile or more along the bluffs 

 no Cooper is present. In eastern Moniteau County along the 

 river bluffs the conditions are about the same as in Boone County. 

 Along the Lamine River in Cooper and Pettis counties the forma- 



