THE TERTIARY TO THE MODERN PERIOD. 229 



abundant on the shores of the Great Slave Lake and on 

 the McKenzie Kiver, and according to Eichardson con- 

 stitutes much of the drift timber of the Arctic coast 

 (Fig. 78). 



6. Thuja occidentalism Linn. Trunks and branches 

 in the Leda clay at Montreal. This tree occurs in New 

 England and Canada, and extends northward into the 



Fig. 78. — Populus balsamifera. Pleistocene, Canada. 



Hudson Bay territories. It is a northern though not 

 arctic species in its geographical range. According to 

 Lyell it occurs associated with the bones of Mastodon in 

 New Jersey. From the great durability of its wood, it is 

 one of the trees most likely to be preserved in aqueous 

 deposits. 



7. Potamogeton perfoliatus, Linn. Leaves and seeds 

 in nodules at Green's Creek. Inhabits streams of the 

 Northern States and Canada, and according to Eichard- 

 son extends to Great Slave Lake. 



8. Potamogeton pusillus. Quantities of fragments 

 which I refer to this species occur in nodules at Green's 

 Creek. They may possibly belong to a variety of P. 

 hybridus which, together with P. natans, now grows in 



