THE SWEETLAND CREEK BEDS 73 



they are due in the section, all the way from Muscatine to Mont- 

 pelier. It is therefore no very difficult task to combine the local 

 outcrops into a general section. 



GENERAL SECTION OF THE SWEETLAND CREEK BEDS 

 Number Feet 



7. Dark bituminous shale, occasionally containing small flat concre- 

 tions of iron pyrites, with three thin bands of greenish shales 

 respectively about 5, 9, and 12 feet from the base - - - 33 



6. Dark shale, with thin seams of blue shale, the dark containing two 

 species of lingula, Spathiocaris emersoni, Rhynchodus, and a 

 fossil resembling Solenocaris strigata - - - - - 3 



5. Greenish shale, with occasional stony layers, containing flat con- 

 cretions of pyrites frequently bordered by lamellar marginal 

 extensions of a white dolomitic material - - - -3% 



4. Alternating layers of greenish stone and green and dark shale, the 

 latter in part containing a network of thread-like extensions of 

 the former. The green shale has elongated flattened concretions 

 resembling fucoid growths and lying parallel with the bedding. 

 The stony layers are frequently charged with small grains of 

 pyrites and contain minute fragments of fossils - - 2 



3. Greenish fine-grained argillaceous magnesian limestone impreg- 

 nated with iron pyrites and calcium phosphate, in ledges from 4 

 to 10 inches in thickness, with cylindrical fucoid impregnations 

 slightly more greenish than the matrix and from 3 to 6 milli- 

 meters in diameter, containing two species of lingula, a frag- 

 mentary cast of a helicoid gasteropod, and imprints of some 

 fibrous structure like that of some plant stem - - - Z% 



2. Hard greenish-gray shale, with a stony pyritiferous layer that con- 

 tains fish teeth and impressions of vegetable tissue about 10 

 inches from base ---------3 



1. Argillaceous dolomitic stony layer containing Ptychtodus calceohis 



and other forms resembling Synthetodus - - - % 



Litliological peculiarities. — The greenish ledges turn grayish- 

 yellow on weathering. The main stony ledge, number 3, often 

 protrudes as a shelf over the clay below it, which is more easily 

 removed by erosion. In two instances an efflorescence of 

 epsomite was noticed forming on the face of the clay thus pro- 

 tected from rain by the overhanging rock. The material found 

 in the shells of the lingulas of this ledge was unaltered, but 



