614 Characteristics of the Insect-Fauna 



between the fauna of the iipj)er and that of the lower 

 regions, and considerable collections have been made for 

 the sake of illustrating such distinctions ; on the present 

 occasion, however, I propose to limit myself to a few in- 

 stances drawn almost exclusively from the Diurnal Lepi- 

 doptera. 



One feature in the vegetation of the White Mountains 

 strikes the most casual observer in an instant, — the ab- 

 rupt limits of the forest growth upon the sides of the 

 mountains, marking a very natural division into a wooded 

 and a woodless district. This latter district, on a nearer 

 approach, will, to the observant eye, disclose a further 

 separation into two regions : a lower, where the dwarfed 

 spruce, struggling upwards, conceals the gray rocks in a 

 covering of uniform green, save upon the unstable surfaces 

 of the steeper slopes, or where the land-slips have scarred 

 the declivities with their lengthened furrows ; and an up- 

 per, more restricted area, in which the barren blocks of 

 stones lie piled in inextricable confusion upon one an- 

 other, exposed to full view, unrelieved by any grateful 

 coat of green, except by an occasional patch of sedge 

 upon some more favored level spot. These three areas — 

 the forest district, the district of the dwarfed spruce, and 

 the rocky district — exhibit, in a general way, as I believe, 

 the proper limits of the mountain, the subalpine, and the 

 alpine regions ; the separation of the mountain from the 

 subalpine region is well marked by the limit of the trees, 

 which is not wholly dependent upon llie elevation of the 

 slope upon which they grow, being influenced in part by 

 the ravines which vary the uniformity of their lines, and by 

 the exposure of the sides of the mountain, causing a vari- 

 ation of from one to two hundred feet in perpendicular 

 height. Upon Madison, and the northern sldpe of Wash- 

 ington, the forest line, as shown by the measurements of 

 Prof. Guyot, reaches to the height of 4150 feet ; and upon 



