BRADLEY: BRACHIOPODA OF THE MAQUOKETA OF IOWA. 505 



A marked lithologic change is observed in all places at the boundary 

 between the Galena and ]Maqiioketa. Whether the IMaquoketa was 

 preceded by a 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 jNIaquoketa have a bed of yellow clay between them, a sugges- 

 tion of erosional unconformity. 



Litholodic Character: — Although much variation in composition is 

 tj^ical of the ^^laquoketa, dark bluish gray clay-shale predominates. 

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

 one locality it outcrops as dolomite and limestone to a thickness 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. Clermont 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. 



LiNGULA BELTRAMI \Yinchell and Schuchert. 



Lingula beltrayni WincheU and Schuchert, Geol. Minn., 1S93, 3, pt. 1, p. 351, 

 fig. 25 a, b. 



A single incomplete specimen representing parts of ])oth valves 

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

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



