PAPERS OX GEOGRAPHY AND GEOLOGY 247 



basins in which there accumulated the sediments that 

 make up the Fernvale limestone. This sea transgressed 

 far to the north and northwest, overlapping the former 

 areas of Maquoketa, and united with the northern sea 

 in northwest Illinois, northeast Iowa, and Wisconsin and 

 Minnesota. In this sea there was a mingling of the 

 aboriginal or older Maquoketa faunas with the invading 

 faunas from the south. However, the invading species 

 were dominant and left the strongest impress on this 

 youngest fauna of Richmond age in the Maquoketa basin. 

 It is thought that these uppermost calcareous and very 

 fossiliferous strata of the Maquoketa were deposited be- 

 fore the invasion of the sea from the northeast into the 

 Indiana-Ohio basin which occurred during upper AYay- 

 nesville time. A late Richmond sea advanced from the 

 south into Illinois and Missouri, in which was deposited 

 the Thebes sandstone which rests unconformably upon 

 the Fernvale limestone at Thebes, Illinois, and Cape 

 Girardeau, Missouri. This Thebes sandstone deposition 

 may have taken place at the same time the sandy sedi- 

 ments of the Saluda member were deposited farther east, 

 but it was probably somewhat later. The non-f ossi- 

 ferous shale that in places overlies the calcareous and 

 fossiliferous horizon in the Wilmington, Minooka, and 

 Maquoketa areas described in this paper was probably 

 deposited at the time of the Thebes submergence. 



