C. E. Gordon— Keokuk Beds at Keokuk. 295 



could be reconciled with the symmetry of the crystals from 

 New Almaden, the southern district. 



It is through the kindness of Mr. Waldemar Lindgren of 

 the U. S. Geological Survey and Mr. F. Yon Leicht, the super- 

 intendent of the New Almaden quicksilver mines, that the 

 material was available for this study. 



Laboratory U. S. Geological Survey, Washington, D. C, June, 1890. 



Art. XXXIX. — On the Keokuk Beds at Keokuk, Iowa • by 

 C. H. Gordon. 



The exposed area of the Keokuk Beds is nowhere extensive. 

 Their relations to the adjoining beds— the Burlington below 

 and the St. Louis above — are everywhere marked by strict 

 conformity, their separation being based solely upon lithologi- 

 cal and faunal distinctions Of these, the faunal characteris- 

 tics especially are of such a nature as to mark this formation 

 as one of the most important of the Lower Carboniferous 

 group. The exposure at Keokuk is limited, being entirely due 

 to the erosion of the Mississippi river and its small tributaries. 

 Along the borders of these the limestone of the lower division 

 usually presents a bold and smooth escarpment. 



Outside of the Keokuk region where the beds were first 

 studied, the most notable exposures occur at Orawfordsville, 

 Indiana, and in southwestern Missouri. At the former locality 

 they are 280 feet thick with a distinctively crinoidal and mol- 

 luscan fauna,* In Missouri they contain valuable deposits of 

 lead. 



The general dip toward the south and west carries these beds 

 from sight just below the mouth of the Des Moines, but a 

 change of dip again brings them to view in the vicinity of 

 Quincy, 111., and at other places to the south. In some cases 

 their appearance is due to faulting. 



At Keokuk these beds consist of two well-defined divisions 

 — the Lower or Calcareous and the Upper or Geode division. 



II. Geode Bed or Division. 

 13. Fine, blue sandy layer. Crinoid bed No. 3. Resem- 

 bles the arenaceous layers of the crinoid bed at Craw- 

 • fordsville, Ind. Seldom seen. Seventeen species of 

 Poteriocrinido?, Batocrinns lagunculus Hall, B. inter- 

 medins W. and S., B. sindlis Hall, B. originarins W. 

 and S., B. mundidus Hall, Taxocrinus Wortheni Hall. 

 Thickness 6 in. 



* American Geologist, vol. ii, p. 407. 



Am. Jour. Sci.— Third Series, Vol. XL. No 238.— Oct., 1890. 

 19 



