26(3 CAKHONIFKKOUS FOKMATIONS AND KAUNAS OV COLOKADtJ. 



woro in a mcasiiro expressed by Cross and Spencer in their n^port upon the geology 

 ol' till' Rii'i) Mduntnins." Considering- the Rico fauna in the light of later evidoncu; 

 and further stiulios, 1 am disposed to think that I placed its ago distinctlj' too late in 

 the Kansas section. 



In my early effort to correlate the Rico formation, which residted in assigning 

 it to about the horizon of the Neosho and Chase formations of the Kansas section, 

 the lines of evidence chiefly considered were the relative abundance of the brachio- 

 pods to the true MoUusca, and the range in the formations discussed by Prosser of 

 such genera and species as seemed to have special significance. Prosser, as is well 

 known, treated only the upper portion of the Kansas section,'' and the evidence of 

 individual genera and species in the matter of correlation proved rather conflicting. 

 Considerable weight was given the relative representation of the brachiopods, because 

 their gradual disappearance seemed an important feature in the changes which 

 marked the progression fi'om the Wabaunsee to the Maiion fauna. I held the 

 opinion at the time, however, that this circumstance would be of only local signifi- 

 cance unless it proved to be a part of the far-reaching vital changes that resulted in 

 the extinction of nearly all the Paleozoic types of brachiopods. 



Later publications upon the earlier faunas of the Kansas section and further 

 studies of my own have made it possible to reconsider the faunal evidence of the 

 Rico upon a somewhat different basis, but with a result nearly as unsatisfactory. 



Except for 0/ionetes mesoloius the brachiopods of the Rico afford no evidence in 

 point, for Seniinula subtilita, Productus nehraskensis, Product-m cora, and Choneten 

 glaher range from bottom to top of the Kansas series. Olionetes mesolohus, however, 

 there appears not to pass beyond the Parsons limestone (No. 6). On the other 

 hand, in the Sinbads Valley collection, the horizon of which is supposed to be below 

 the Rico, we have characteristic Enteletes hemvplicatus, which does not appear in 

 Kansas until the lola limestone (No. 16), and Chonetes granulifer, which is first seen 

 in the Lecorapton limestone (No. 22) 



Among the Rico pelecypods are a few forms whose evidence may be considered. 

 Pseudomonotis equistriata first appears in Kansas in the lola limestone (No. 16), 

 Pseudomonotis hawni in the Eskridge shales (No. 37), and Pseudomonotis hansasensis 

 in the Garrison formation (No. 39). Myalina subquadrata, like Pseudomonotis equi- 

 striata^ is introduced in the lola (No. 16), and Bulimorpha chrysalis, like Pseudomo- 

 notis hawni, in the Eskridge shales (No. 37).° 



The absence of Bakewellia is to be noted in the Rico fauna, which should hardl}' 

 be correlated with the top of the Kansas section (Marion formation), nor yet with its 



a U. S. Geol, Surv., Twenty-first Ann. Kept., pt. 2, 1900, pp. 15-166. 



dJour. Geol.. vol. 3, 1895, pp. 682-705 and 764-800. Geol. Soc. Am.. Bull., vol. 6. 1895, pp. 29-54. Jour. Geol., vol. 5, 

 1897, pp. 1-16, 148-172. Kansas Univ. Quart., vol. 6, pp. 149-175, 1897. 



t-'Tlie range of species in the Kansas section can not be regarded as completely known, and the statements above are 

 only approximations. 



