THE BARITE DEPOSITS OF MISSOURI 37 



oolites show several well developed zones, but have no nucleus. 

 The central part of some is dark gray crystalline quartz. In 

 polarized light the areas between the oolites show the dark cross 

 characteristic of chalcedony. The outer band or zone is more 

 coarsely crystalline than any of the other zones, and is the same 

 as the chalcedony surrounding the oolite. Thins sections of the 

 dolomite adjacent to the oolitic chert in the same bed showed 

 original structures that could be interpreted as oolites which 

 now are replaced by anhedral grains of dolomite. 



Another type of chert of unusual interest is one that appears 

 to be oolitic but is merely composed of well rounded fragments 

 of chert, many of them almost spherical. These were thought to 

 be oolites at first but the unusual size of some that were found 

 later showed that such was not the case. The microscope con- 

 firmed the conclusion that they were merely rounded fragments 

 of chert. 



Most of the fossils in the Gasconade formation are in the 

 chert. They are well preserved but are very difficult to get out 

 in perfect condition. They are gasteropods and fragments of 

 orthoceras. 



Beds of chert-breccia at least three feet in thickness appear 

 in the lower part of the Gasconade formation. Their exact hori- 

 zon is not known, for very few exposures of more than a few 

 feet were seen. The breccia weathers out in large masses, some 

 of them are as large as 10 by 6 by 3 feet. It consists of angular 

 fragments of bluish-gray, translucent chert, up to four inches in 

 diameter, which are embedded in a dense white chert. The frag- 

 ments lie at all angles in the matrix. 



The dolomite and chert members of the formation are per- 

 sistent, but the sandstones are lenticular. There are sections of 

 the Gasconade formation more than 200 feet thick in which not a 

 single sandstone bed appears. In other places, sandstone beds 

 are numerous and show all the characteristics of such beds. 

 They are rarely continuous for more than a few miles, and most 

 of them pinch out in less than one or two miles. 



Some of the dolomite is very thin-bedded, there being beds 

 of a half inch or less in thickness, and those of two to four inches 

 are common. Some beds are several feet thick, but this is not 



