THE BARITE DEPOSITS OF MISSOURI 21 



been moved by sliding. The pebbles are all more or less rounded, 

 showing water action, and the horizontal position of the majority 

 of them shows that they were deposited by water. They were 

 undoubtedly formed in shallow water after the muds have been 

 partially hardened. The waves then broke up the crust, partially 

 rounded the fragments, and buried them in a carbonate mud. 



Upper part of the Elvins. — Beds that Buckley called the 

 Derby and Doerun formations are here regarded as the Upper 

 Elvins for reasons given later. They are dolomites or slightly 

 calcareous dolomites from top to bottom. There are some shaly 

 beds, but these are relatively free from more than a thin film of 

 clayey material. No sandy lenses were observed in the area 

 along Big River or Mineral Fork like those in the dolomites in 

 the southeastern corner of the area. The prevailing color is some 

 shade of gray, a light gray shade greatly predominating, altho 

 occasionally some beds are bluish-gray. Near the top of the for- 

 mation the beds are buff, the topmost layers having a distinctly 

 pinkish cast. Mottled beds are rather numerous, and the mottl- 

 ing is due to dark bluish-gray nodules of dolomite in a matrix of 

 soft light gray dolomite. These darker parts are sections of 

 fucoids. 



The beds vary in texture from very dense, fine-grained dolo- 

 mites to coarse-grained ones. The majority are fine to medium- 

 grained and have a distinctly granular appearance. Some of the 

 beds, especially those in the upper part of the formation, are 

 very soft and porous, the pores ranging from a fraction of a 

 millimeter to three millimeters in diameter. The buff colored 

 beds near the top are especially characterized by porosity. The 

 porous beds contain many small grains of limonite, which indi- 

 cates some previously existing pyrite. 



The beds are rather pure dolomite, and, like the lower part 

 of the formation, contain occasional areas of calcite which 

 weather faster than the dolomite. 



The beds range in thickness from an inch to 8 or 10 feet, 

 the thickest beds being near the top. A peculiar undulatory 

 structure was observed in these beds. The structure resembles 

 large ripple marks, 10 feet from crest to crest, with an amplitude 

 of 2 feet. The crests are composed o£ hard reddish-gray dolo- 



