THE ILLINOIAN ICE INVASION 



295 



The Florencia formation passes through these rock gorges, completely burying 

 their flat bottoms. Its age is, therefore, not earlier than the practical comple- 

 tion of these gorges. The Florencia formation is overlain with perfect con- 

 formity by the basal member of the Iowan loess series. " 



The drift sheet called Kansan by Hershey is now correlated with the Illi- 

 noian 6 ' drift-sheet and the Florencia formation thus falls into the Sangamon 

 Interglacial interval. Hershey states that typical upland loess occurs above 

 these deposits. This latter formation possibly includes both Illinoian and 

 Iowan loesses. The Florencia deposits are said to be rather widely distributed 

 in the Pecatonica basin and they are believed by Hershey to be represented in 

 other parts of northwestern Illinois. 



The fauna from the Florencia formation is large and varied, including 

 both terrestrial and fluviatile species. It is not specifically stated by Hershey 

 whether some of these came from the old soil (muck). It is a common exper- 

 ience to find land shells in the shore debris mixed with the more common 

 fluviatile shells, tho they by no means occur in such abundance. The list of 

 terrestrial shells seems unusually large, tho there is no reason why these species 

 should not occur in shore debris. They have no connection with the loess. 

 The species listed by Hershey are tabulated below: 



Indian Garden Locality 

 Plenrocera subulate 

 Vivipara species, juv. 

 Campeloma decisiim 

 Amnicola limosa porala 

 " cincinnatiensis 



Bythinella lenuipes 

 Valvata tricarinata 

 Physa helerostropha 

 Ancylus tardus? 



" rividaris 



" parallelus 



Planorbis bicarinatus{ = anlrosus) 



" parvus 

 Galba humilis modicella 



Sphaerium slamineum 

 striatinum 



Crane Creek Locality 

 Plearocera subidare 



Campeloma decisum 



Amnicola cincinnatiensis 

 Somatogyrus depressus 

 Bythinella tenuipes 

 Valvata tricarinata 

 Physa heterostropha 



Segmantina armigera 

 Planorbis antrosus 

 parvus 



Galba obrussa 

 Sphaerium slamineum 



striatinum 



simile{ = sulcatum) 



solidulum? 



Pisidium walker i 



" cruciatum 

 " fallax 



Pisidium fallax 



ec Leverett, Illinois Glacial Lobe, p. 167. 



