420 Tarr — Origin of the Chert in the Burlington Limestone. 



The chert occurs chiefly in the form of I'oiinded, elliptical, or 

 lenticular nodules (see fl^. 5). The nodules are found always 

 with their longer axes parallel to the bedding planes hut they 

 are not necessarily along them, although such is a common 

 occurrence. Rarely the lenticular masses merge so that the 

 chert becomes essentially a bed. This is not a very common 

 feature in the Burlington in this vicinity but in other localities 

 it becomes a very important mode of occurrence, especially in 



Fig. 5. 



Fig. 5. Banded chert nodules in Bnrlingion limestone, 

 The notebook is 5^ inches long. Stylolite at (a). 



Columbia, Mo. 



the lower Paleozoic formation, where thick beds occnr. Along 

 a given plane the nodules are of a remarkably nniform size, 

 but there are marked variations in size along the different 

 planes. The rounded nodules are rarely more than six inches 

 in diameter with a range of fron] three to six inches. The 

 elliptical forms are from three to fifteen inches in thickness 

 and from five to twenty-five inches in length. In gi'ound plan 

 the nodules are very irregular, but the dominant tendency is 

 tow^ards a lobed circnlarity. The lenticular nodules may vary 

 from two to fifteen inches in thickness and some reach a length 

 of several feet, as can be seen in figures 5, 6, and 7. Elliptical 

 and lenticular forms are dominant. 



The layers of chert nodules may occur along such bedding 

 planes as the limestone shows, or they may occur at various in- 



