RELATIONS OF FAUNAS TO ENVIRONMENT. 29 



o 



Missouri arc now limited, the lower Burlington forms still flourished in 

 the waters to the southwest ward j even as far as the present boundaries of 

 New Mexico. 



In regard to the derivation of the Keokuk fauna from the areas con- 

 siderably east of the Mississippi river line and of the Burlington from 

 districts west of that limit, a further hint is obtained in an examination 

 of the various faunas that immediately preceded. Again the crinoids 

 may come into service. Attention already has been called to the pecu- 

 liarly fitting role that the stemmed echinoderms play in considerations 

 of this kind, and to their ornamentation and general structural charac- 

 ters as shown in the three members of the Osage. Composed of regular 

 plates, definitely arranged and often highly ornamented, delicate pinnu- 

 lated arms, and characteristic stems, these organisms were admirably 

 adapted for recording the changes in the physical conditions of their 

 environment. The species of the Devonian and the early Carboniferous 

 in the eastern portion of the Mississippi basin were, with few exceptions, 

 large, massive, heavily plated forms, coarsely ornamented, and possess- 

 ing in many cases a peculiar extravagance of structure. An examination 

 of the species from the Kinderhook and the accessible Devonian of the 

 western district shows that in great part the forms were all highly and 

 delicately sculptured, rather frail in construction, and of small size. There 

 seems to be but little doubt that in the district of southeastern Iowa the 

 Burlington forms are genetically related to those of the subjacent dej m >sits. 

 The relationships of the same forms to those of tire rocks immediately 

 above has always appeared to be only in part genetic. The apparently 

 direct succession is explicable in many cases on the assumption (which 

 is very probable) that the barrier alluded to above was only partial, 

 allowing a certain amount of mingling. The lithological characters of 

 the strata immediately heneath the Burlington also attest the shallowness 

 of the water along the line mentioned. 



Warsaw Beds. — The Warsaw beds, as defined by Hall :|: and as exposed 

 at the village of Warsaw, Qlinois, are composed of (1) 10 feet of com] tact, 

 buff-colored limestone. C_') 30 feet of blue calcareous shales with many 

 thin limestone seams, and (•".) 8 feet of yellow arenaceous limestone. At 

 Keokuk, live miles above, all three layers are thinner, and at neighbor- 

 ing places they exhibit still different characters. Southward the beds 

 Lose their argillaceous nature and appeal' not to be separable from the 

 associated Limestones. These layers, together with the geode bed, which 

 is usually considered the upper member of the Keokuk, may be regarded 

 as mere local developments to which Little importance is to be attached. 

 In a quarry a short distance northwest of Rand park, at Keokuk, Iowa, 



HJeolog) "i town, pt. i, LS58 p U7. 



