4:18 Tarr — Origin of the Chert in the Burlington Limestone. 



of glauconite ; and a small amount of a yellowish, dust-like 

 material, wliicii is probably clay. 



D. MODE OF OCCURRENCE OF THE CHERT. 



The Burlington limestone, of lower Mississippian age. is in 

 this region from 100 to 175 feet in thickness. It is a heavy, 

 irregularly bedded, coarsely crystalline limestone, mainly of a 

 light bluish-gray color. The upper portion in some parts of 

 Missouri is line-grained and the lower is coarse-grained. The 

 beds are not well defined, due evidently to a lack of silts, etc., 

 in the waters and to rapid variation in the sizes of the calcare- 

 ous materials. The beds are rather tliick, but range from a 

 few inches to several feet. The formation consists dominantly 

 of the remains of crinoids, in fact crinoids are so abundant that 

 the formation was formerly known as the " Encrinal limestone." 

 The chert occnrs throughout the formation but is especially 

 abundant in the lower half near the top. The following sec- 

 tions of the Burlington at different localities in Missouri will 

 show the distribution of the chert: 



Section of Burlington limestone one half mile south of Columbia, 



Missoi^ri. 



Limestone: medium to coarse-graint d; gray; con- 

 tains stylolites and a few chert nodules 3 ft. 6 in. 



Limestone: medium to fine-grained; gray. This is 

 a very cherty zone; contains large masses of 

 chert and considerable pyrite in small nodules; 

 the large chert masses occur along planes 13 ft. 6 in. 



Limestone: coarse, medium, and fine-grained; usu- 

 ally some shade of gray, bluish tints predom- 

 inating; fossiliferousin places; sty lolites rather 

 common .. 13 ft. 



Limestone: coarse-grained; fossiliferous; blue gray ; 

 contains st) lolites, and chert nodules along a 

 plane . . 4 ft. 



Limestone: fine-grained, gray, stylolitic 2 ft. 



Limestone: coarse-grained, grading upwards into 

 fine-grained; blue gray to buff; contains chert 

 in large nodules and is stylolitic. 2 ft. 



Limestone: fine-grained and medium to coarse- 

 gi'ained; blue gray; contains stylolites and 

 chert ... 2 ft. 



Chert: man}^ large nodules along this plane 2 ft. 



Limestone: medium to fine-grained, the texture 

 varying rapidly both vertically and laterally; 

 gray to blue gray; fossiliferous; contains styl- 

 olites and scattered nodules of chert 6 ft. 6 in. 



Limestone: coarse-grained; light to very dark 



gray; stylolitic 1 ft. 6 in. 



Limestone: medium to fine-grained; gray; has nu- 

 merous stylolites . _ 2 ft. 



