BRADLEY: BRACHIOPODi 01 rHE tfAQUOKETJi 01 [OWA. 505 



A marked lithologic change is observed in all place ;ii the boundary 

 between the Galena and Maquoketa. Whether the Maquoketa wos 

 preceded l>> ;i period of erosion is still uncertain. In Dubuque County , 

 Iowa, no erosion of the Galena can be noticed and no unconformity. 

 At Graf, on the other hand, the Galena dolomite and the blue shale 

 of the Maquoketa have a bed of yellow clay between them, 8 -ml 

 lion of erosional unconformity. 



Lithologic Character: Although much variation in composition is 

 typical of the Maquoketa, dark bluish gray clay-shale predominates. 

 Tin- formation may occur as a single undivided body of shale. In 

 oik' locality it outcrops as dolomite and Limestone to a thick ne- of 

 forty feet. In northern Iowa the formation falls naturally into four 

 members: — 

 4. Brainerd shale. 



Blue and bluish gray shale with strata of limestone inter- 

 bedded at top and bottom. 120 feet. 

 3. Fort Atkinson limestone. 



Massive yellow cherty dolomite with associated beds of 

 limestone. 40 feet. 

 '2. ( lermont shale. 



Bluish, plastic, fine-grained shale, well developed at Cler- 

 mont, Iowa. 15 feet. 

 1. Elgin shaly limestone. 



Limestone, dolomite, shaly limestone with beds of calcareous 



shale and thin partings of bluish less calcareous clay that are 



variable in character and fossil content. 



This division, unfortunately, does not persist throughout the 



formation. A division into three members seems to be the more 



universally applicable although this is not a hard and fast rule. 



Lixgulidae. 

 Lixgula beltrami Winchell and Schuchert. 



Lingida beltrami Winchell and Schuchert, Geol. Minn., 1893, 3, pt. 1, p. 351, 

 fig. 25 a, b. 



A single incomplete specimen representing parts of both valves 

 was obtained from the Lower Maquoketa at Clermont. The condi- 

 tion of preservation is not such as to justify any special description. 



