108 CONTRIBUTIONS TO THE GEOLOGY OF MAINE. [bull. 165. 
600 feet, with an average slope of about 50°. The last 100 feet is very 
steep, and the whole appearance leads one to recognize the appropri- 
ateness of the name by which it has long been known. The base of 
the main mass covers scarcely more than one-fourth of a square mile, 
but connected directly with it is a narrow ridge of the same volcanic 
material extending about three-fourths of a mile to the northwest. 
The easiest ascent is on the north side, where, on account of the con- 
nected ridge, the slope is scarcely over 30° until the top is neared. The 
east and the west sides are very precipitous. The talus on the slopes 
is abundant and is, in general, made up of small angular fragments, 
although on the west side there is a confused mass of giant blocks so 
piled as to leave large, roomy spaces between and underneath, which 
are locally called caves. Higher on the slope these detached pieces 
are more and more in place, until near the top blocks weighing 40 tons 
and more are found separated from the main mass by deep cracks a 
few inches wide and are ready to be pried off by the frosts of winter. 
The top of the hill is an uneven surface covering less than one-fourth 
of an acre, and an examination of the rock there exposed reveals the 
presence of a complicated system of intersecting cleavage cracks which 
has determined the form and size of the loose blocks on the slope. As 
one walks about the base of Haystack or climbs to the top, attention 
is attracted by the varied appearance of the materials composing the 
mass. On the top, only the dense bluish-white felsitic rock appears. 
Halfway down the slope the surface exposures have the peculiar birch- 
bark appearance which characterizes parts of the white rhyolite. At 
the southeast base of the hill occur little knobs which are formed of a 
dark breccia with jasperlike fragments embedded. Near by is the 
variety of rlryolite made up of little spherules; and finally, about one- 
half mile east of the hill, there is a well-marked vesicular lava. A 
detailed description of these various forms of rocks will be found in 
the chapter on petrography (pp. 146-186). 
From the field relations alone it is no easy matter to determine the 
character of this igneous mass. Only the top part is free from trees, 
underbrush, and moss, which conceal the rocks and make traveling 
difficult. The talus covering is very deep and widespread, and the 
drift has been so deposited as to conceal the contacts. Consequently 
the exact relation between the igneous and sedimentary rocks is not 
known. There does not seem to be much metamorphism except in 
places to the east of the mountain. The character of the rocks, how- 
ever, is conclusive, for the} T are undoubtedly flows of lava, and indicate 
by their amygdaloidal structure nearness to the surface of flow. The 
probable field relation is indicated diagrammatically by the accom- 
panying cut (fig. 3). 
The whole mass has either been formed by some very recent extru- 
sion or is the remnant of more extensive flows which have been long 
