578 W. W. DAVIS 



crinoidal remains, mostly stems, and (b) the presence of numerous 

 specimens of Spirifer with plicated fold and sinus. 



The fauna of the bowlders. — These bowlders are abundantly 

 fossiliferous, but the fossils are largely fragmentary and are com- 

 monly poorly preserved. Unfortunately they are nearly all in the 

 form of molds, a condition of preservation which has added to the 

 difficulties of their identification. None of the fossils are silicified, 

 but a few of the cavities left by the solution of the shells are 

 sprinkled with crystals of pyrite and dolomite. The extremely 

 weathered portion of the rock is generally too soft to yield deter- 

 minable fossils, and the unweathered portions yield comparatively 

 few. The great majority of the better specimens have been 

 collected from the partially weathered portions. 



The most abundant fossils are the crinoids, although most of 

 the specimens are mere fragments of stems, few of which can be 

 identified even generically, and they are of little scientific value 

 except to show that the rock has been a conspicuously crinoidal 

 limestone. Next to the crinoids the brachiopods are the most 

 common fossils, and owing to their abundance and better state of 

 preservation they form the most satisfactory element of the whole 

 fauna. Besides the crinoids and the brachiopods the fauna con- 

 tains corals, blastoids, bryozoans, pelecypods, and gastropods, 

 none of which are represented by numerous species or specimens. 



The composition of the fauna is shown by the accompanying list 

 of species that have been identified (Table I). The number of 

 examples of each species that has been observed is recorded after 

 each name for the purpose of showing the relative importance 

 of the several members of the fauna; the geologic range and 

 geographic distribution are shown in the several columns. 



The geographic and geologic relationships of the fauna. — The 

 geographic and geologic relationships of this fauna are not difficult 

 to determine. Considering first the brachiopods, the list shows 

 that all the forms are found in the Mississippi Valley, although a 

 few species have a wider range. Of these brachiopods, two species, 

 Spirifer gregeri and Spirifer mundulus, are Lower Burlington. 

 Three species, Dielasma burlingtonensis , Spirifer forbesi, and 

 Spiriferella plena, are confined to the Burlington. Seven species, 



