FAULT SYSTEMS IX IOWA 



109 



bottom of the excavation is nearly, if not quite, down to the St. 

 Louis formation; and is about thirty feet above the level of the 

 water in the Des Moines river near by. Fully seventy feet of 

 shale are exposed in clean section, which presents the following 

 sequence of beds: 



SECTION AT CLAY-PIT OF FORT DODGE BRICK AND TILE 



PLANT. 



Feet 



9. Till, ashen, with pebble bands 15 



8. Shale, blue, yellow and variegated 18 



7. Sandstone, gray, massive 2 



6. Shale, black and gray, with coal-seams 11 



5. Shale, white (fire-clay) 2 



4. Shale, light-colored and variegated 15 



3. Shale, dark-colored, partly hidden at base 25 



2. Sandstone, coarse, conglomeratic, ferruginous 1 



1. Limestone, gray 30 



In cross-section, the ridge appears as represented below 

 (figure 6), in which the gypsum-plate is noted to lie about thirty 

 feet beneath the level of the top of the adjoining St. Louis lime- 



Port Dodge 



Bride & T'ilejf 



Pit £-. 



CC'oa.l Measure: 

 .-.---. "shales 

 70' 



Miocene: 



Shales-^ 

 ^75' 



Fig. 6 — Details of Fort Dodge fault. 



stone, and nearly one hundred feet beneath the top of the coal 

 measures of the clay-pit. In stratigraphic level there is thus a 

 discrepancy of more than one hundred feet between correspond- 

 ing parts on the two sides of the ridge. 



On the west face of the ridge, in a railway cutting, near a 

 point where on the same level the pink shales appear to be ab- 

 ruptly replaced by the dark shales of the coal measures, an in- 

 consequential faulting of the first mentioned beds is plainly 



