WANLESS— LITHOLOGY OF WHITE RIVER SEDIMENTS. 201 



Thus it seems that while the White River may be mainly of eolian 

 origin in Colorado as Matthew has decided, it was mainly deposited 

 by fluviatile agents in the South Dakota section. The writer's con- 

 clusion is that in the sections of the Big Badlands investigated eolian 

 deposition is unimportant, though locally present. 



VI. Evidence of Ground Water Circulation. 



Though the clay beds of the Badland district seem to be nearly 

 impervious to water, there are abundant evidences of deposition and 

 replacement by the action of ground water. The formation of caliche 

 nodules by deposition of calcareous cementing material with the evap- 

 oration of the water at the surface has been referred to. 



Throughout the Big Badland district are veins of blue chalcedony 

 in vertical cracks in the clays. These were probably deposited in 

 shrinkage cracks. Other fissures filled with sandy silts or sandstones 

 occur frequently through the Badlands, but most abundantly in the 

 Leptauchenia beds. These filled fissures are often more resistant 

 to weathering than the surrounding clays and stand out in relief as 

 sandstone dikes. Often the sandstone dikes were bordered on each 

 side by chalcedony veins, and in one case there were two or three 

 veins of chalcedony on the same side of the dike, indicating repeated 

 opening of the fissure. The chalcedony veins ordinarily vary in 

 thickness from one quarter inch to three inches and show evidence 

 of gradual filling of the cracks from the two walls. Sometimes the 

 whole vein is silica, but in many cases, specially in the wider veins, 

 well-formed crystals of calcite have formed in the center of the vein, 

 evidently as the last stage of deposition. Sometimes the center of 

 the vein remains open. Occasionally large bell-shaped concretions of 

 chalcedony up to a foot in diameter are formed in the clay. Chal- 

 cedony of similar nature is found filling the marrow cavities of fossil 

 bones and the pulp canals of teeth. An interesting case was noted 

 by the writer in a bone in which the lower part of the marrow cavity 

 was filled with fine silt, evidently worked in soon after deposition, 

 and the rest of the cavity was filled with chalcedony. In several cases 

 chalcedony veins were found to cut directly through fossil skulls. 

 Generally no hardening of the clays adjacent to the chalcedony veins 

 is observed, showing that the deposition was from cold water. Some 



