1910J Bruncken, .Studies in Plant Distribution. 149 



the spring. Their influence will be noticeable in retarding the be- 

 ginning of the growing season, while they tend to increase the 

 relative moisture of the air, by which transpiration is regulated. 



The proximity of so large a body of water has, of course, the 

 usual effect of reducing temperature maxima. This is true es- 

 pecially of the beach and terraces. On the bank, the steepness of 

 the slope is the cause of greater insolation, and thereby the influ- 

 ence of the water is counteracted to an undetermined degree. 

 The increase of soil temperature caused in this manner would be 

 even greater, if most of the slopes were not of an easterly or 

 northeasterly exposure. In places where the exposure is more 

 towards the south, the greater xerophily of the vegetation is quite 

 marked. 



The ravines, though more shaded, are often warmer than the 

 beach and terraces. The difference is very noticeable during hot 

 summer days, as one steps from the sultry atmosphere of the ravino 

 out on the open shore. The difference is undoubtedly due to the 

 absence of air currents in the ravines, which allows a heating up 

 of the atmosphere by radiation. During cool weather, the difference 

 is far less, and the relation may even become reversed. 



C. The Historical Factors. 



The changes which have taken place in the area may readily 

 be divided into three classes, not peculiar to the locality, but applic- 

 able everywhere. The first of these includes all changes in physi- 

 ography and climate due to purely physical causes. It is well es- 

 tablished that there was a somewhat complicated series of changes 

 in the water level of the Lake, following the recession of the last 

 continental glacier."' In the course of these vicissitudes, forests 

 were covered with water and finally buried in mud, as shown by 

 the large extent of buried forest areas in the state. What may 

 possibly be parts of these forests are now being uncovered by the 

 erosion of the Lake Shore banks, as will appear below. As to 

 climatic changes, we are still very much at sea regarding the 

 climate prevailing during the latter part of the Glacial and in the 

 Champlain period, and consequently are unable to say what 

 changes may have taken place. 



The second historical factor is biological. No matter how well 



3) Geol. Survey W r is., vol. I, page 292. 



