0. IT. Ilershey — Flovencia Formation. 95 



side of the Rock river valley, would seem to connect it with 

 the Iowan epoch. Therefore, we cannot with full confidence 

 refer its age to either epoch, but may perhaps more properly 

 consider it as occupying a transitory stage between the Aftonian 

 and Iowan epochs.* 



Fauna. — Collections of shells have been made from two 

 principal localities. The first is in the bank of Yellow creek 

 about 100 feet east of the Chicago, Milwaukee & St. Paul 

 Railroad bridge, and is referred to as the Indian Garden locality, 

 the name having been derived from a popular designation of 

 the peninsularly shaped body of land enclosed by the creek in 

 the great bend which it makes in the vicinity of the mouth of 

 Crane creek. Great care was taken in securing the shells 

 that they actually came from the Florencia formation and not 

 from Modern silt and muck which might have been deposited 

 on the former by the present stream. An excavation was 

 made into the bank and the fossils secured from under the 

 loess which appears higher in the section. No mistake can 

 have been made, as the strata of blue-green silt, light brownish 

 gray sand and dark muck which everywhere in this region 

 form the upper division of the formation, were here present 

 with all their characteristic features, and the shells were taken 

 from undisturbed or originally stratified portions of them. 

 This care was taken because it was early recognized that a 

 fauna of a very similar facies occurs in the Modern alluvial 

 deposits, and the two might easily be confounded. 



The second place from which collections were made is the 

 Crane Creek locality. Here the same care was taken as in 

 making the other collection. I do not think there is a possi- 

 bility of a mistake having been made, as the blue-green silt 

 is typically developed and the loess appears in unmistakable 

 form above it. 



These collections of Florencia shells were submitted to Dr. 

 W. H. Dall of the IT. S. Geological Survey, who has identified 

 them as in the following lists : 



* Since this discussion of the stratigraphic relations of the formation was 

 written, I have become aware of the establishment of a new classification of the 

 Illinois and Iowa drift. This applies the term " Aftonian " to an interglacial stage 

 preceding the formation of the Kansan drift-sheet. It, also, establishes a new 

 sheet of drift intermediate in position between the Kansan and Iowan sheets; 

 this is designated the Illinoian drift-sheet. As it is now doubtful which sheet is 

 exposed in Stephenson County, Illinois, and what term should be applied to the 

 long deglaciation interval following, my use of the words " Kansan " and 

 "Aftonian " should be considered as tentative, and relative to the term " Iowan." 

 This will not affect the " age " of the formation, which undoubtedly belongs 

 immediately before that of the Iowan loess series. See editorial in American 

 Geologist, vol. xix, No. 4, April, 1897. 



