THE ILLINOIAN ICE INVASION 



329 



lake was at first about that of the present Lake Ontario (possibly somewhat 

 lower), but later rose to 60 feet (Don beds) and finally to 150 feet above the 

 present level (Scarboro beds). This change of level was due probably to the 

 rising of the outlet at the east end of the Ontario basin (differential elevation). 



Previous to the formation of the Don beds the underlying Illinoian boulder 

 clay had been eroded by streams to a depth of 15 feet (the lower portion being 

 in shale rock). A rich forest of deciduous and coniferous trees had also 

 migrated northward, and the mammoth, mastodon, and bison roamed the coun- 

 try. The great variety of this forest covering is indicated by the number of spe- 

 cies of plants which have been found in this deposit. These are listed below: 



Acer pleistocenicum 



" spicalum 



" torontonensis 

 Asitninia triloba 

 Carya alba 

 Cercis canadensis 



Ckamaecyparis sphaeroidea ( — thyoides) 

 Chara species 

 Clethra alnifolia 

 Crataegus punctata 

 Cyperaceae species 

 Eriocaulon species 

 Fraxinus americana 



" sambuciformis ( = nigra) 

 " quadrangulata 

 Festuca ovina 

 Gleditsia donensis 

 Hippuris vulgaris 

 Hypnitm species 

 Juniperus Virginians 

 Larix americana { — laricina) 

 Maclura aurantiaca ( = pomifera) 



Ostrya virginica 



Picea nigra (=mariana) 



" species 

 Pinus strobus 

 Platanus occidentalis 

 Popnlus balsamifera 



" grandidentata 

 Primus species 

 Quercus alba? 



' acuminata { = muhlenbergerii) 



" macrocarpa 



" oblongifolia 



" obtusiloba ( = stellata) 



" rubra 



" tinctoria ( = velutina) 

 Robinia pseudo-acacia 

 Salix species 

 Taxus canadensis 

 Thuja occidentalis 

 Tilia americana 

 Ulmus americanus 



" racemosa 

 Vaccinium uliginosum 



Of the above species three are extinct, Acer pleistocenicum, A. torontonensis, 

 and Gleditsia donensis. The waters of the interglacial lake teemed with mol- 

 lusks, over 40 species having been recorded, as noted below: 



Pelecypoda 



Fusconaja undata ( = trigona) 



" solida 

 Crenodonta undulala 

 Quadrula puslulosa 



pustulosa schoolcraftensis 

 Pleurobema coccineum 

 pyramidatum 

 " clava 



Gastropoda 



Campeloma decisum 

 Pleurocera elevatum 



elevatum leivisii? 

 " subidare 

 Goniobasis depygis 



haldemani 

 Somatogyrus isogonus 

 A mnicola limosa 





