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



E. AGE OF THE CHERT. 



The question as to the time of the formation of the chert is 

 a very important one in considering its origin, since the major- 

 ity of the theories, and especially the commonly accepted one, 

 appeal to the action of circulating ground water in accounting 

 for the chert. If it can be shown that the chert is of a certain 

 age, the time necessary for its formation can be estimated. 

 This period of formation would be the time extending from 



Fig. 9. 



Fig. 10. 



Fig. 9. Cracks in chert filled with limestone. 



Fig. 10. Limestone from above a chert nodule, showing ridges which 

 once partly filled the cracks in the chert nodnle (see fig. 11). 



the deposition of the limestone to the present, if the chert 

 was formed by circulating ground waters. That the chert is 

 pre-Pennsylvanian in age is shown by the following facts. It 

 is a very abundant constituent of the Turke}^ Creek conglomer- 

 ate at the base of the Pennsylvanian in Callaway County, 

 Missouri. This chert contains an abundance of Burlington 

 fossils, and, therefore, it must have been formed previous to 

 the erosion of the Burlington in pre-Pennsylvanian times. 

 Similar conglomerates are reported by Ball and Smith in their 

 report on the geology of Miller County, Missouri, and by Buck- 

 ley in his report on the Granby district in the Joplin zmc 

 region. 



In the vicinity of Columbia, Missouri, there are numerous 

 solution cavities in the Burlington limestone which are tilled 

 with chert fragments imbedded in Pennsylvanian shales and 

 muds that had been washed into the cavities. Both of the 

 foregoing facts indicate that the chert in the Burlington lime- 

 stone was formed in pre-Pennsylvanian times, and that it ante- 



