DISTRIBUTION OF THE BURLINGTON 61 



rapidly southward, and this movement was soon followed by 

 slight depression. The Saint Louis watersCthen pushed north- 

 ward again, in some places several hundred miles. 



Burlington Limestone — The lithological characters of the 

 Burlington limestone are remarkably constant over broad 

 stretches of territory. At the original locality it is a coarse- 

 grained encrinital limerock; hard, compact and heavily bedded 

 in some layers, porous in others, with scarcely enough of firm 

 and cementing material to hold the crinoidal remains together. 

 In some places, however, it is very compact, fine-grained and 

 earthy, and is then reddish or deep brownish in color. Chert 

 nodules abound locally. The lower portions are usually much 

 more heavily bedded than the upper — the partings of the in- 

 ferior beds being commonly a coarse, calcareous reddish sand, 

 while in the upper strata, clay seams are not infrequent. 



In western Illinois, in Pike and Marion counties, Missouri, 

 in the southwestern and central portions of the same State, the 

 lithological nature of this formation is the same. (Plate vii, 

 hills capped by Burlington limestone.) In Greene county, in 

 the southwestern part of Missouri, the upper and lower divi- 

 sions are as well marked faunally as they are in southeastern 

 Iowa. In fact, the two divisions at both localities are in all 

 respects so near alike, that a person investigating and collecting 

 at Springfield and Ash Grove could not tell but that he was in 

 the environs of Burlington city itself, if he did not actually know 

 that he was nearly 300 miles away. But the Burlington fauna, 

 in all its entirety, is found much farther to the south. westward — 

 as far at least as the Lake Valley mining region of New Mex- 

 ico, though there the lithological. characters of the strata are 

 somewhat different. For the most part the geographical distri- 

 bution of the Burlington limestone is west of the Mississippi 

 river. East of the stream the typical exposures of the rock 

 are unimportant, and unknown beyond the immediate vicinity 

 of the great water-course. 



In the most northeasterly counties of Missouri a shallow 

 syncline carries the Burlington limestone below the level of 



