UX roW'A ACADKMV OF .scf k..vcf:». 



allows conrsoly tlic costiitc^ stru^'tare <it" Sijilhirfa. 'Vhi' ;ir- 

 faiiu-omont of the nreolcs caiiiurt Ik» made out t]iou«>h [)r()l) i- 

 l)ly distant and not continuous. As stated by Lesquereux tlie- 

 flccovticated layers are (rf little if any speeifi' value, hut tlu!- 

 fiet that, so far as we can learn, tliis f(>rni.:i,ti{)n his thus far 

 proven destitute of land [)lants o-ives this ex un[)le peculiar 

 interest and on this account a name may [)r()ve serviceable. 

 We therefore designate it Siriilhtrki trallacii, in honor (>f it- 

 tinder. 



CVAHJ^rACM. IKVKIZON AND L(K ALITV. 



From the Keokuk limestone six oi- eii>-ht feet bchtw the 

 hase of the Geode bed; found in the t)lu{f just below the Keo- 

 kuk and Des Moin(>s depot, Keokuk, Iowa. 



ON THE KEOKUK BEDS AND THEIR CONTAINED 

 FOSSILS IN THE VICINITY OF KEOKUK, IOWA. 



l;V PKOF. r. H. GORDON. 

 AltKA AM) THICKNESS. 



Outside the region covered by this paper, the most uotal)ie 

 exposure of this formation occurs at Crawfordsville, Indiana, 

 where its thickness is said to he two liundred and eiijhtyfeet. ' 



'-ioiitli of the Iowa line, exposures o''cur aloni^- the Missis- 

 sip[)i in limited areas, and southwestward in ^lissouri, yield- 

 iui>- most of the lead mined in that ren'ion. 



At Keokuk it consists of two well defined divisions — the 

 lower or Calcareous and the upper or (icodc division. The 

 Calcareous division consists of forty t(» sixty feet of limestone 

 in varyini:' layers, with clay or shale parting's one to six 

 inche:^ thick. About the middle of this division occurs a 

 l)ure massive layer termed the "white ledge"" which furnished 



I — Aniefican tleologist, Vol. II, p. vT- 



[Pkoc. 1. A. S., 1887-9. I 9S [March 10, 1890.J 



