574 



PHYSICAL GEOGRAPHY. 



dian plants climbing into the alpine district, it is not strange that the smaller number 

 of boreal species should in like manner spread themselves even into AUeghanian 

 townships. 



The Boundary between the Alleghanian and Canadian Dis- 

 tricts. 



In order to show the near correspondence of the dividing line between 

 the Alleghanian and Canadian districts, according to the several methods 

 of distinction that have been suggested, I annex a map showing the 

 course of the following lines, first, — the broad band settled upon by Mr. 

 Scudder as separating the insects of the two faunae ; second, the upper 

 line of the white oak ; third, the approximate contour line of six hun- 

 dred feet elevation ; fourth, the isothermal line of fifty degrees for April, 

 May, and June. It will be seen, by referring to the map showing the 

 distribution of forest trees, that the chestnut limit does not fall much 

 behind that of the white oak, the whole area occupied by it being colored. 



The upper limit of the white oak extends above the six-hundred-feet 

 contour line as far as Plymouth, from the south line of the state ; may 

 agree with it for a few miles in the lake region, but extends farther north 

 in the Pemigewasset and Saco valleys. In the lower part of Carroll 

 county there is an area above six hundred feet. I do not think the facts 

 are known with sufficient precision to state the presence or absence of 

 the oak in this area. There are other limited areas of greater height 

 not indicated, as the Gunstock region, where the oak certainly does not 

 flourish. Along the Connecticut the limit of the oak reaches as far 

 as the contour line ; while in the south-west part of Cheshire county the 

 reverse is true. Were it legitimate to strike an average in this case, it 

 could truly be said that the two lines correspond very well. There may 

 be special reasons in every case of variation for the spread of the tree 

 beyond or within the Umits of the contour, derived from the character 

 of the soil or particular topographical features, which might be discov- 

 ered upon investigation. Somewhat similar variations appear upon ex- 

 amining the isothermal line of fifty degrees for the three months of 

 April, May, and June, proposed by Prof. Verrill as the limit between the 

 Canadian and Alleghanian birds. This line runs up to Berlin on the 

 Androscoggin, may touch Jackson and Bartlett on the Saco, curving 

 round the southern White Mountains to pass up to Thornton and War- 



