104 LIFE OF THE PLEISTOCENE 



condition — warm-cold temperate-ice. The deposits at Chicago and Toronto, 

 taken together form an almost continuous cycle of an interglacial interval. 



The biota listed in the previous tables also present a perfect picture of the 

 ecology of this ancient bay, the plant and animal communities reflecting the 

 varying physical conditions as the water became shallower or deeper. As has 

 been stated by Shimek, to interpret accurately the species entombed in these 

 clay and sand beds, and to reconstruct the environment in which they lived, 

 the student must have an extensive and varied acquaintance with the same 

 animals as they are found today. 



In the tables the change of types from the shallow water Bowmanville 

 stage to the deeper water Calumet-Toleston stages, and from these to the 

 shallower Hammond and Englewood stages is very marked, irrespective of 

 climate. The first stage (36 species) had a silty, muddy bottom, supporting 

 pond types of naiades and cyclads, and the fresh water pulmonates which 

 usually inhabit such stations. A few gill-bearing mollusks were also present. 

 The second stage (35 species) had a sandy or gravelly bottom, the water was 

 deeper, and there was a change to the river type of naiades, the deeper water 

 cyclads (for the most part) and a few gill-bearing species. The fresh water 

 pulmonates were entirely absent. The third stage (58 species) shows a shallow- 

 ing bay, the bottom becoming muddy. There was a total absence of the river 

 type of naiades and a return of the fresh water pulmonates. The number of 

 cyclads present is noteworthy. The fourth stage (26 species) shows a return to 

 deeper water with a sandy or silty bottom, inhabited by a few cyclads and gill- 

 bearing species, with fresh water pulmonates. There was a total absence of 

 naiades. The fifth stage was probably a land surface with a few creeks. No 

 life has been observed from this stage. In the sixth stage (17 species) the bay 

 had become still shallower, the life consisting of a few cyclads, a very few gill- 

 bearers, and a number of fresh water pulmonates. The bottom was covered 

 with mud and fine silt. The seventh and last stage is of the present time (13 

 species) the water has receded and the surface has become dry land with a 

 few small ponds and swampy streamlets. Here the molluscan fauna consists 

 of pulmonates, with a very few cyclads. The ecological succession shown by 

 these seven stages is approached in completeness only at Toronto, Canada, 

 where a somewhat similar alternation of strata occurs. 



The vertebrates of the Chicago deposits, while not numerous in species, 

 are of great interest, and include fish (3 species), birds (1 species), and mam- 

 mals (5 species). We can imagine the waters teeming with fish life, the pres- 

 ence of ducks on the surface of the lake and bays, and the deer, mastodon and 

 mammoth roaming the shores, while squirrels chased one another among the 

 tree tops. It is also probable that the caribou, musk ox, snow goose, and other 

 tundra animals inhabited the region, and during warmer times the peccary 

 may have lived here, as its remains have been found in Ohio, Michigan, and 



