NO. 1850. KXOBSTOXE CRINOID FAUNA— SPRINGER. 179 



relations, it makes considerable difference whether a given species is 

 said to be derived from the Keokuk Limestone or from the lower beds 

 of the BurUngton or the Kinderhook, for these stand for the extremes 

 in what is probably the best, and best preserved, Hne of local crinoid 

 development in all geological history. The Biirhngton and Keokuk 

 beds represent the acme of crinoidal life, both in variety of form and 

 profusion of individuals, and it was the overwhelmingly predominant 

 faunal feature of those epoclis. So profuse is its development that it 

 has been proposed by Wachsmuth and Springer and by Keyes to 

 recognize this by grouping the two formations into a distinct division 

 of the Lower Carboniferous, for wliich Keyes ^ proposed the name 

 ''Augusta," and Williams, before him,^ \\ith slightly different limita- 

 tions, that of ''Osage." 



Of more importance than tliis, however, is the fact that faunal 

 considerations have required us to further subdivide it, so as to 

 recognize the upper and lower beds of the Burlington as well marked 

 and distinct horizons. There is a thoroughly well-defined succession 

 in the crinoidal fauna, beginning in the Lower Burlington with a 

 predominance of species characterized by great delicacy of form and 

 beauty of ornamentation, and culminating in the Keokuk with 

 prevalent forms of large size, rough ornamentation, and much exag- 

 geration of structural details, in many cases marking the extinction 

 of the genera. Between these there is a distinctly intermediate con- 

 dition, represented by the Upper Burlington. The three formations 

 are separated by heavy transition beds of chert, each marking the 

 extinction of most of the species and some of the genera of the bed 

 preceding it, and the inauguration of a rougher habit in the forms 

 which follow. ' These facts were pointed out long ago by White,^ 

 Wachsmuth and Springer,* and Keyes. ^ The modifications here indi- 

 cated do not apply to all the species, some simpler forms of a more 

 generalized type persisting through the beds with little change, while 

 in some there was a distinct retrogression, resulting in ultimate extinc- 

 tion through diminished vitality. But in the specialized and pre- 

 dominant types, like Camerata, the process of acceleration and abrupt 

 termination from one bed to another and at the close of the epoch 

 was most striking. 



The focus of this profuse development of crinoidal life was the 

 region near and west of the Mississippi River, in Iowa, Illinois, and 

 Missouri. It was a deep and clear water formation, little disturbed 

 by oscillation or other causes, and continuous through a long period, 

 except for the changes produced by the repeated increase in the 



■ Iowa Geological Survey, vol. 1, 1892, p. 61. 



2 Bull. 80, U. S. Geol. Surv., 1891, p. 109. 



3 Joum. Boston See. Nat. Hist., vol. 7, 1860, pp. 224-225. 

 * Proc. Acad. Nat. Sci. Philadelphia, 1878, p. 229. 



6 Geol. Surv. Iowa, vol. 1, 1893, p. 65. 



