62 NEW YORK STATE MUSEUM 



and subsequent fires, the -latter of frequent recurrence on some 

 areas, has resulted in a more or less complete change of vegetation 

 and in the production of conditions which has favored the spread of 

 sand-loving species of herbs and shrubs. (Figure 5.) 



Geology. The only portion of geological history which is of con- 

 cern here is the Quaternary Period, including the great Ice Age and 

 the subsequent changes in drainage which have taken place in central 

 New York, and especially of Oneida lake which lies in a depression 

 of the southeastern lobe of the Postglacial Lake Iroquois, which 

 discharged its waters to the east through the Mohawk valley. Dur- 

 ing the retreat of the ice sheet in this region, the St Lawrence valley 

 was still buried under the ice. 



Much later the ice sheet retreated sufficiently to allow the discharge 

 of the water along the northern base of the Adirondacks and into the 

 Champlain and Hudson valleys and finally retreated far enough to 

 free the St Lawrence valley and lower the surface of Lake Iroquois so 

 that Oneida lake became isolated from the main body of Postglacial 

 waters, and its drainage was turned from the Mohawk to the Oswego 

 river. Higher levels of Oneida lake are plainly marked by ridges of 

 sand east of the present western shore line which are similar to the 

 low ridge of sand now existing within the fringe of vegetation 

 (figure 6) along the shore, and caused by the action of high water 

 and strong westerly winds. 



Climatic influences. The influence of the waters and low eleva- 

 tions of the Great Lakes region serves to produce a distinct climatic 

 province with longer growing season than any other part of the State 

 except the lower Hudson valley and coastal islands. It is a well- 

 known fact that large bodies of water absorb more heat, hold more 

 heat, are warmed to greater depths and absorb and radiate heat 

 more slowly than land areas. In addition to this, probably half of 

 the insolation on water areas is used in evaporating water, and 

 since the prevailing winds of the Ontario lowlands are westerly, 

 the total effect of these conditions is to make cooler summers, milder 

 winters, to prolong the fall season and to retard spring as well as 

 to check to some extent sudden changes in temperature. 



These climatic influences are reflected in the character of the 

 vegetation of the Ontario lowlands, where the prevailing forest trees 

 are oak, hickory, chestnut, tulip-tree, elm, basswood, ash, black 

 gum and sassafras, while of infrequent occurrence except in bogs 

 are spruce, tamarack, balsam and white cedar. 



This apparent Austral influence is reflected in the character of 

 the forests of the Ontario lowlands as far eastward as the lowlands 



