GEOLOGY OP SOUTHWESTERN IOWA 529 



PsaiT Inches 



9. Limestone, light gray, weathered yellow 8 



8. Shale, weathered 6 



7. Limestone, blue, weathered yellow 16 



6. Shale, yellow 2 



5. Shale, blue 7 



4. Limestone, gray, impure and shaly, in three layers 1 



3. Shale, weathered 1 



2. Limestone, bluish gray, one layer cut by veriical 



joints into large rhombohedral blocks 2 



1. Limestone, blue, weathered brown, broke-i into 



small blocks 1 



Total 16 8 



If the Fusiilina layer of the Tarkio is present here it is now 

 conoealed by slumping. Doctor Calvin seems to have found it ex- 

 posed. Numbers 1, 2, 3, 4 represent the Preston and 7, 8, 9 the 

 Tarkio. In a part of the outcrop there is exposed seven feet of 

 Nebraskan drift, crumbly black clay, diagonally jointed, contain- 

 ing; pockets of sand and small pebbles of white chert. Eighty 

 rods north of the creek bridge, along the roadside, is seen the 

 Kansan drift, very arenaceous, containing diabase and quartzite 

 gravel and bowlders of Sioux quartzite. Several fragments of 

 friable Cretaceous sandstone were found which could have not 

 been transported in a drift sheet from ledges far distant. 



At Coburg in the blufif east of the village there is an excellent 

 exposure of Cretaceous sandstone. It was examined by Lonsdale 

 twenty years ago and is still in good condition. 



SECTION IN BLUFF EAST OF COBURG. 



Feet 



3. Shale, light gray, in wagon road cut, south of pit 11 



2. Conglomerate, quartz pebbles, arenaceous limonite matrix, 



dark brown 8 



1. Sandstone, yellow, cross bedded, friable, with streaks of 



gravel 24 



Total 43 



In the deep road cut about one hundred yards south of the 

 sandstone pit the ferruginous conglomerate is overlain by eleven 

 feet of light gray, poorly bedded shale giving a thickness of 

 forty-three feet of Cretaceous strata in this bluff. Eighty rods 

 south of the w^agon road a quarry was opened many years ago 

 which now is much obscured. Immediately under a light cover- 

 ing of drift five or six feet of the Cretaceous conglomerate is 

 seen in place. The quarry was opened in Carboniferous lime- 

 stone underneath the conglomerate. No undisturbed layers of 

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