THE TERTIARY TO THK MODERN PERIOD. 231 



from its present flora, though it might contain the same 

 species found in the nodules, would certainly include with 

 these, or instead of some of them, more southern forms. 

 More especially the halsam poplar, though that tree oc- 

 curs plentifully on the Ottawa, would not be so pre- 

 dominant. But such an assemblage of drift-plants might 

 be furnished by any American stream flowing in the lati- 

 tude of 50° to 55° north. If a stream flowing to the 

 north, it might deposit these plants in still more northern 

 latitudes, as the McKenzie Eiver does now. If flowing 

 to the south, it might deposit them to the south of 50°. 

 In the case of the Ottawa, the plants could not have been 

 derived from a more southern locality, nor probably from 

 one very far to the north. We may therefore safely as- 

 sume that the refrigeration indicated by these plants 

 would place the region bordering the Ottawa in nearly the 

 same position with that of the south coast of Labrador 

 fronting on the Gulf of St. Lawrence at present. The 

 absence of all the more arctic species occurring in Lab- 

 rador should perhaps induce us to infer a somewhat 

 milder climate than this. 



The moderate amount of refrigeration thus required 

 would in my opinion accord very well with the probable 

 conditions of climate deducible from the circumstances in 

 which the fossil plants in question occur. At the time 

 when they were deposited the sea flowed up the Ottawa 

 valley to a height of 200 to 400 feet above its present 

 level, and the valley of the St. Lawrence was a wide arm 

 of the sea, open to the arctic current. Under these con- 

 ditions the immense quantities of drift-ice from the 

 northward, and the removal of the great heating surface 

 now presented by the low lands of Canada and New Eng- 

 land, must have given for the Ottawa coast of that period 

 a summer temperature very similar to that at present ex- 

 perienced on the Labrador coast, and with this conclusion 

 the marine remains of the Leda clay, as well as the few 



