HISTORICAL REVIEW 7 



to any modern species, though the former approaches P. sikhensis, and the 

 latter Q. falcata and Q. primus. " 



"The genus Picea (spruce) does not now grow within several hundred miles 

 from the locality, and the species of oaks which are now found upon the sur- 

 face of the ridges are neither falcata nor primus. The indication is that 

 previous to the beginning of the Recent beach, a climate and flora prevailed 

 like that in Alaska. Then when the peat began to form at the time as indi- 

 cated by the peat layer at 4, the spruces had disappeared and a species of oak 

 had taken their place, and now these have disappeared and other oaks have 

 replaced them. This lower soil in the section at A, lying upon the clay, indi- 

 cates a time when the surface of the waters were as low relatively to the land 

 at this place as now. Afterwards the waters rose as high as the Upper beach. 

 After the Upper beach was formed, the waters subsided to the Middle beach, 

 and again to the Recent beach. The coniferous wood probably grew before 

 Lake Michigan was definitely formed. 



"The oak is not completely decayed. The outside wood of the trunks is 

 spongy, but the central portions are tough and fibrous. Borers then as now 

 infested the trees. 



"Horizon 5, just above the peat, marks the upper or later limit of the 

 Mastodon. It was on this soil about six years ago that the bones of a mastodon 

 were found in Chicago, on the south side of Wicker Park near Milwaukee 

 Avenue. They were covered by thirteen feet of silt, or as Dr. Andrews sug- 

 gests, loess. The bones consisted of part of a jaw, teeth, and parts of a few 

 other bones, and are now in the collection of the Chicago Academy of Sciences. 12 

 There is in the Museum of the College of Liberal Arts of the Northwestern 

 University a fragment of fossil ivory received from the late James L. Milner, 

 afterward connected with the U. S. Fish Commission, taken from a gravel pit 

 excavated in the Middle beach in Evanston when the Milwaukee Branch of 

 the C. & N. W. R. R. was constructed. From what level it was taken, is 

 not now known. The pit appears to have been excavated to the clay, and the 

 fossil was probably on the same stratum as that at Chicago. 



"There is no positive evidence that the waters of the lake were salt water 

 at the time the Upper beach was deposited. No shells have been found in the 

 beach by which the character of the waters could be determined, but the 

 presence of sea shore plants now upon the lake shore, and the existence of the 

 marine Mysis in the waters of the lake, indicate that at some time, salt water 

 has existed where Lake Michigan now is. 13 The old bay of the lake whose mar- 

 gins are marked by the Upper beach, left some silt on its bottom, and in these 

 silts have been found fresh water Unios. We have fragments of such shells 



12 A careful search has failed to reveal the specimens mentioned. 



13 This statement is not bome out by later investigations. There is no reason to believe 

 that the waters of the lake were ever salt. 



