286 PROCEEDINGS OF THE ACADEMY OF [1889. 



feet of gray, compact and oolitic limestones. The upper part of the 

 great arenaceous bed is charged with casts of brachiopod and 

 lamellibranch shells ; it also contains a number of gasteropods and a 

 few pteropods. A similar sandstone ten feet above presents like 

 fauna! peculiarities. The fossils of the calcareous layers are usually 

 in an excellent state of preservation, especially those occurring in 

 the oolites: and it is from the latter that the most satisfactory 

 material for serial comparisons is obtained. 



The Burlington limestone is pre-eminently crinoidal in its com- 

 position. It includes also several extensive beds of siliceous shales 

 and cherts. The greater portion of this division is composed of thick- 

 and thin-bedded limerock, the layers of which are frequently 

 separated by clayey or sandy partings. Alternating with the firmer 

 strata are often great beds of coarse friable rock made up almost 

 wholly of the disjointed and comminuted skeletal remains of 

 echinoderms. In all observable characters — stratigraphic, faunal 

 and lithologic — the two member- of the Lower Carbonic at Burling- 

 ton present a very marked contrast, The most distinctive feature, 

 perhaps, is the great preponderance of crinoidal remains in the upper 

 part ; while in the lower, or Kinderhook, there are but few traces 

 of the feather stars. 



Attempts have been made at various times to subdivide the 

 Burlington limestone into upper and lower sections; the chief basis 

 for separation being the difference in the crinoid fauna? contained. 

 While in the ensemble there is a very noticeable dissimilarity in the 

 general expression of the species of the two divisions there is not, 

 as is claimed, a totally distinct group of forms in each. Recent 

 observations indicate that a considerable proportion of the species 

 in the Lower Burlington are also present in the Upper; and even pass 

 with some slight structural modifications into the Keokuk. With 

 the material already accumulated, the transit ionary relations of 

 the various species have been traced; and there appears to be but 

 little doubt that the respective fauna? of the two members were the 

 biologic successors of one another, at least in the region of south- 

 eastern Iowa. It has further been shown recently : that the limestone 

 of the continental interior, usually denominated the Burlington and 

 Keokuk, practically belong to a single epoch. 



Briefly summarized, the general faunal features as set forth in the 

 following pages indicate very different bathymetric conditions during 



i Kejes: Am. Jour. Sci., (3j, vol. XXXVIII, p. 186. 



