FILLMORE COUNTY. 801 



Maquokcta shales.] 



35, York. At Lime Springs, Iowa, the great shale bed which sheds water, 

 causing the springs which gave name to the place, is supposed to be the 

 Maquoketa. 



Besides the foregoing points, the outcrop of shaly rock about a mile 

 east of Spring Valley, exposed by the grading for the Southern Minnesota 

 railroad, presents various interesting features. The fossils here seen con- 

 sist in part of Orthis testudinaria, Dal., 0. subquadrata, Hall, Lynx, Eich., 

 plicatella, Hall, subcequata, Con., amoema, Winch, and Whitfieldi, Winch.; also 

 Strophomena fluctuosa, Bill., and Leptcena sericea, Sow., as well as some forms 

 of Chcetetes, and of crinoids, indicating sufficiently the Lower Silurian age 

 of the strata. These can be picked up in considerable numbers on the 

 sloping surface which was scraped to obtain the loam for the railroad 

 grading. This is on the north side of the track, but at a point a little 

 nearer Spring Valley these beds are also exposed on the south side in the 

 same way. In passing toward Spring Valley depot the grade descends a 

 little, and reaches the spring-bearing horizon which has given origin to the 

 name of the village. At the same time the argillaceo-magnesian strata 

 of which but little can be seen at one mile east of the depot, are brought 

 out more conspicuously, and are seen in outcrop on the north side of the 

 valley at several old quarries that have been abandoned. Here these beds 

 contain large specimens of Strophomena alternata ( ?), Leptcena sericea, Sow., 

 and a small Rhynchonella that has not been named. But a little higher, in 

 order of actual level, are the coarse cavernous magnesian layers on the 

 south side of the valley, in the highway near the school-house, that have 

 been parallelized with the Lower Devonian.* The actual superposition 

 cannot be seen, but it is not possible for many feet of strata to intervene 

 between them and the recognizable Lower Silurian strata. The general 

 section at Spring Valley may be arranged as follows in descending order: 



Section at Spring Valley. 



1. Coarse magnesian strata, containing Atrypa reticularis, Spirifer and other shells ; 



in 01 terop only on the south side of the valley by the school-house, - 4-6 feet. 



2. Argillo-magnesian strata containing Orthis alternata (?) and Leptcena sericea and 



Strophomena fluctuosa, Bill., in outcrop on the north side of the valley at the 

 abandoned quarries, in the northwest part of the village, and slightly at the 

 railroad cut about a mile east, 20 feet. 



3. Shaly and argillaceous, containing numerous species of brachiopods of the Trenton 



period ; seen at the railroad cut, and probably underlying the village, causing 

 springs by its impervious nature. Under it are the limestone beds burnt for 

 lime on Deer creek. - Thickness unknown. 



*See the Mower county report. 



