96 T. 8. Hunt on Lithology. 
rates by other joints into rectangular blocks, The second 
—_ includes about nine square miles in the township of Shef- 
, to the northwest of the last, and at the nearest point is 
ils: about two miles removed from it, This is known as Shef- 
ford mountain. 
The rocks of these ~ mountainous areas present but very 
slight differences, being, so far as examined, everywhere made 
up in great part of a pe feldspar, with small pores ~ 
brownish-black mica, or of black hornblende, which are som 
times associated. The proportion of these two minerals is ed 
above a few hundredths, and is often less than one hundredth, 4 
The other mineral species are small brilliant crystals of yellow- 
ish sphene, and others of magnetic iron, amounting together 
probably to one thousandth of the mass, In some finer-grained s 
varieties a few rare crystals of sodalite and of nepbeline are met 
with. But for the uniform absence of quartz, these rocks might = 
be taken for varieties of granite and syenite. They are very 
friable, and subject to disintegration, so that the soil forsome = 
distance anal these mountains is almost entirely made up of 
the separated crystals of feldspar, which however show but little 
tendency to decomposition, and retain their lustre. The rockis 
sometimes rather finely granular in its texture, but is often com- 
posed of cleavable masses of orthoclase, which are from one-fifth 
one-half of an inch in breadth, and sometimes nearly an inch =| 
in eokth The lustre is vitreous, and in the opaque varieties, 
pearly ; but the crystals never exhibit thee eminently glassy lustre 
nor the fissured appearance that characterizes the feldspars i 
many Saropsas trachytes which are similar to them in compo- 
tion. The color of the feldspar of these rocks is white, passing __ 
into reddish on the one hand, and into pearl-gray or lavender: 
gray on the other 
Specimens of the rock of Brome mountain were taken from 
the side near to the village of West Shefford. It was coarsely 
crystalline, lavender-gray in color, and contained a little brown 
mica, sphene, and magnetic iron, but no hornblende. The den- 
sity of fragments of the rock was found to be 2°632-2°638. 
grains of the paeal at had a specific gravity of 2°575, and 
gave by analysis the result 1. The analysis of a sage uh speci 
men from another portion of the hill, is given under 
e rock ee e south side of Shefford cena ats next 
mined. Ino art it consisted of a coarse grained grayish 
tl scribed from the adjace nt mountain. A little 
aia) na the hill, however, was a variety which, though com 
se ae more coherent — ner grained —_ 
nat or - hier dspar_ rarely exhibiting cleavage-planes- 
a fourth of < inch in length. Brilliant crystalline 
