VERMONT. 109 
age much inferior to that of the sea-green shite and somewhat inferior to thai of the 
Eureka of the unfading green. There are about 6 chlorite plates, interleaved with 
muscovite, to each square millimeter, measuring up to 0.087 by 0.043 millimeter 
and lying at right angles to the cleavage. Quartz fragments are very abundant, 
measuring up to 0.06 by 0.03 millimeter, with a few of plagioclase feldspar; mus- 
covite scales in various orientatioi s; a few carbonate rhombs, the usual abundance 
of rutile needles, and, finally, pyrite, which seems to he more abundant in the purple 
than in the green. The purpi ? differs from the green by the addition of hematite. 
The chief constituents, arranged in descending order of abundance, appear to be 
muscovite (sericite), quartz, chlorite (hematite in the purple), carbonate, rutile 
(kaolin in the purple, at least), pyrite, and, as shown by a magnet test, magnetite. 
The specific gravity of the purple from Cedar Point was found to he 2.83 and of 
the green from the J. Jones quarry 2.S4, both being a little higher than the figures 
for any of the other western Vermont slates. 
Slate-pencil date. — In the unfading green-slate portion of the belt, about \\ miles 
north of Bomoseen and a little east of the lake, is an abandoned quarry where cer- 
tain greenish slates were obtained and made into slate pencils. In Europe slate 
pencils have long been made by utilizing a secondary cleavage, which breaks the 
rock up into squarish sticks which are easily rounded. Here, however, the method 
was to take tile-shaped blocks of slate and carve out first on one side, then on the 
other, by means of set gauges, a whole series of hemicylindrical pencils which readily 
broke apart into roundish pencils. A microscopic section of this rock shows essen- 
tially the same composition as the unfading green slates, excepting that sections par- 
allel to the cleavage show no carbonate whatever, but a greater abundance and larger 
scales of muscovite (probably sedimentary) /some limonite ? specks, and a cleavage 
perhaps not quite so good as that of the Eureka quarries. The usual quartz, sericite, 
chlorite, rutile needles, and lenses are present. 
The general substitution of paper tablets for school slates in this country has almost 
stopped the manufacture of slate pencils. 
Minerals associated villi the green and purple slates. — As the minerals of visible size 
associated with the slates throw light on the nature and origin of the microscopic 
constituents of the slate itself, they are here given: 
Quartz is the most common accessory mineral. It is usually segregated in the veins 
already described, but occurs also as an infiltrated cement between the quartz grains 
in the beds of quartzite or in veins traversing the quartzite. In both of these modes 
it is crystallized whenever cavities admit of it. 
Next in abundance is calcit', occurring also in veins with or without quartz, or as 
jdelicate films on joint planes, or as a sediment in the beds of quartzite. Thequartz- 
ite beds sometimes contain minute rhombs which effervesce readily with hydro- 
chloric acid and weather a limonite brown, and are therefore probably a double 
carbonate of iron and lime. 
Squarish or oval concretions an inch by three-fourths of an inch and one-half inch 
thick, consisting of radiating crystalline lamellseof barite, with the intervening spaces 
filled with slate and calcite and with many minute cubes of pyrite round about, occur 
in the Cambrian green slates of .Middle Granville. Barite also oceans with calcite in 
(crystalline films on joint planes. 
Chlorite is common in quartz veins, or almost alone makes up small veins, or coats 
[lickensided joint or bedding planes. 
Pyrite occurs in cubes up to one-fourth inch across or in botryoidal concretions, 
r oated with fibrous quartz (chalcedony) or with calcite, or, more rarely, chlorite. 
This coating of chalcedony is often confined to some of the sides, filling a space pro- 
luced by motion or compression, as described by Renard. Pyrite may collect in the 
vicinity of calcareous and quartzose veins or beds, or form dendritic crystallizations 
