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



nodules (see tig. 3). This is a feature wliicli would have de- 

 veloped in a band if the material in which it is found had 

 undergone a certain amount of movement laterally. Since 

 these broadened parts of the bands are always found in those 

 portions of the nodules which must have moved laterally if the 

 nodule has been tiattened, it is believed that they were caused 

 by such a movement. The widened portions of the bands are 

 usually of a lighter color than the narrower ones, showing that 



Fig. 7. 



Fig. 7. Shows chert nodules along a plane in Burlington limestone, 

 Columbia, Mo. 



in the former the same amount of coloring matter has been 

 distributed over a wider zone. When circular nodules contain 

 bands, the bands do not show this widening. 



The majority of the nodules show upon their surfaces many 

 cracks (see ^^^. 8, 9, and 10) which may be three inches in 

 depth and one-half inch in width at the surface of the nodule. 

 They gradually die out in the chert. These cracks are usually 

 filled with limestone which is always continuous with the lime- 

 stone surrounding the nodules (see fig. 11). Many examples 

 of reopened cracks are found. This reopening occurred after 

 the complete consolidation of the beds and the chert. A 

 coarsely crystalline, yellow or white calcite was deposited in 

 these reopened joints. It may occur on one side or on both 

 sides of the limestone in the original crack but is usually on 

 one side only. The limestone which fills cracks may contain 



