PREFACE 



About nine years ago, Mr. A. Scharf, a gentleman interested in the study 

 of Archaeology, discovered a bed of mussels, containing the species Elliptio 

 crassidens, near the old village of Bowmanville, in the northwestern part of the 

 City of Chicago. These specimens were referred to the writer who doubted 

 their having been found near Chicago, the present distribution of crassidens 

 being upwards of a hundred miles from the City, southward and westward. 

 Investigation revealed the presence, hitherto unknown to either the geologists 

 or the zoologists of Chicago, of a fossil deposit of wide extent, which contained 

 not only the species in question but many others, both pelecypods and gastro- 

 pods. These deposits were in a new drainage canal, called the North Shore 

 Channel, which now extends from Bowmanville northward to Wilmette, a dis- 

 tance of about eight miles. 



The writer was fortunate in being able to follow the excavation of this 

 canal foot by foot and thus to secure fresh exposures. During a period of two 

 years the entire length was carefully surveyed with the results described in 

 the pages that follow (Part I). The new Calumet-Sag Channel, draining the 

 southeastern part of the city, was also studied, but in no such detail as was 

 the North Shore Channel. It is greatly to be regretted that this canal, pre- 

 senting quite as important data as did the North Shore Channel, could not 

 have been given equally as exhaustive study. The small amount of time 

 available was used to the utmost and important data were obtained. 



As the work proceeded, it became evident that here was an opportunity to 

 reconstruct the life and conditions of this ancient glacial lake; to ascertain 

 the bearing of this life upon the migration and repopulation of the glaciated 

 area; and to compare the postglacial with the recent fauna and flora. To this 

 end the literature was searched for data relating to this region and much 

 time was spent in different parts of the area in quest of additional material. 

 The study of the Chicago region very naturally led to a consideration of other 

 regions once covered by the great ice sheet and also to other periods of glacia- 

 tion — the little-known interglacial intervals. The result of these studies is 

 embodied in the two parts of this volume. 



Part I embraces an account of the postglacial geology and life of the Chica- 

 go region, and also a resume of our present knowledge concerning the post- 

 glacial life of the entire glaciated region of the United States and Canada. 

 In Part II the life of the interglacial intervals is discussed and the species of 

 plants and animals listed. This is largely a compilation, all available literature 

 having been searched for data. In this part the placing of a record in a parti- 



