166 THE CANADIAN NATURALIST. [^ av 



by the oil-well borings. Between the River Ottawa and the 

 Georgian Bay and Lake Superior, the Algoma sands form a pro- 

 minent feature in the surface deposits, whilst over the Upper 

 Canada peninsula and along Lake Ontario, are chiefly distributed 

 the Erie clays and Saugeen clays and sands. This varied nature 

 of the rock surface, the presence of these very numerous lakes over 

 the Laurentian strata, and the great diversity in the depth as well 

 as general characters of the surface deposits, must have a not 

 inconsiderable influence upon the vegetation of the country, 

 especially in the multiplication or diminution of the numbers 

 of many species. 



In many localities throughout Western Canada, there are 

 terraces and ridges of soil extending over, in some cases, con- 

 siderable surfaces of country — evidences of the much higher levels 

 attained by the Great Lakes and certain rivers in some recent times 

 than exist at the present day. My correspondent, Mr. John 

 Macoun, of Belleville — other of whose careful observations 

 obligingly communicated, are elsewhere in the present paper 

 referred to — has informed me that in his neighbourhood the 

 ridges (the surface soil of which is generally a fine sand slightly 

 mixed with clay, with a subsoil of usually limestone gravel or fine 

 sand) support a vegetation of a southern and western aspect 

 not met with in localities of a different nature in the same section 

 of country. This would appear to be attributable rather to the 

 general nature and state of aggregation than to any particular 

 chemical condition of the materials composing the ridges. When 

 of such loose materials as the sand, clay and gravel referred to, 

 these ridges are always well drained, and where exposed to the 

 action of the sun, absorb the heat with great readiness. This 

 heat in radiating again into space, continues to supply the plants 

 growing upon the ridges with warmth during the intervals of 

 night, Now, much less heat is absorbed, and, consequently, less 

 radiated into the atmosphere by a wet and stiff clay, than by a 

 loose, gravelly, or somewhat sandy soil, and the oxygen of the air 

 has much less access to the organic substances in and the roots ot 

 plants growing upon the soil. These consequences are observable 

 among all our surface deposits, in a greater or less degree in propor- 

 tion to the state of aggregation and general character of their com- 

 ponent materials, and would be similar, though in a less marked 

 manner, if the soil were not in ridges. The rather rare Ranunculus 

 rhomboideus Goldie, Helhmth* emim Ccmadense Michx., and 



