100 SCIENCE 
flint, and plate, the sand is always carefully 
dried before being used. 
In size for ordinary purposes of glass manu- 
facture practically all of the sand grains 
should pass through a 30-mesh sieve, or in 
other words have a diameter less than .64 
millimeters. The majority of the grains should 
be retained on a 120-mesh screen, or be over 
136 millimeters in diameter. For optical 
glass, all of the sand should pass through a 
48-mesh sieve. The shape of the grains has 
little to do with the relative values of the 
sand, although perhaps an angular sand is a 
little more desirable than one in which all of 
the grains are well rounded, other factors be- 
ing equal. 
In 1915, Pennsylvania produced 455,112 tons 
of glass sand. This represents about one 
fourth of the total production of glass sand in — 
the United States. Pennsylvania holds this 
important rank as a producer of glass sand for 
two reasons: first there are found within her 
borders an abundant supply of nearly pure 
quartz sandstones that yield when crushed an 
excellent grade of sand, and secondly the center 
of the glass industry of the United States is 
located in western Pennsylvania so that there 
is a great demand for such sand. Nearly all 
of the glass sand at present produced in 
Pennsylvania comes from two formations, the 
Oriskany of the Devonian and the Pottsville 
of the lower Pennsylvanian. Of these the 
Oriskany is by far the more important. 
The Oriskany formation occupies the belt 
of Appalachian folding which crosses Central 
Pennsylvania and which reaches a maximum 
width of nearly 56 miles. It varies greatly in 
this area both in thickness and in character. 
In Huntingdon and Mifflin counties a pure 
quartz sandstone phase, which has a thickness : 
of from 60 to 200 feet, is particularly well 
developed. In its unaltered state it is a hard 
bluish-gray quartzite made up of interlocking 
grains of quartz in which silica in parallel 
orientation with the original grains is the 
bond. Under favorable conditions of weather- 
ing this has become disintegrated to a friable 
sandstone, or in some places even to a loose 
sand. These are the portions that are used for 
[N. 8. Von, XLVIIT. No. 1230 
glass sand. For this purpose the sandstone 
must be sufficiently friable so that small pieces 
may be broken up between the fingers into 
loose sand. In preparing it for the market 
the rock is passed through a jaw crusher and 
chaser mill or wet grinding pan to disintegrate 
it into loose sand. It is then screened, passed 
through a screw conveyor type of washer, the 
excess water is allowed to drain off, and the 
sand is dried in a steam or direct heat dryer. 
After a final screening it is ready for the 
market. Much of the best grade of glass sand 
produced in the United States comes from this 
district. 
The Pottsville formation of western Penn- 
sylvania is divided into five members as fol- 
lows, commencing at the top: the Homewood 
sandstone, the Mercer shale, the Connoquenes- 
sing sandstone, the Sharon shale, and the 
Sharon or Olean conglomerate. Of these por- 
tions of the Homewood and the Connoquenes- 
sing sandstones are at times sufficiently pure 
quartz sandstones to be available for glass 
sand. The sand derived from them, however, 
is never as pure as that from the Oriskany of 
central Pennsylvania and is, therefore, used 
only in the manufacture of the cheaper grades 
of glass such as bottle and window glass. A 
little is also used in the plate-glass industry. 
The method of treatment is usually the same 
as that used on the Oriskany sandstone in 
central Pennsylvania, except that drying is 
usually dispensed with. Sometimes, however, 
the rock is simply crushed dry and screened, 
washing not being resorted to. 
Cuas. R. FEerrKe 
SCIENCE 
A Weekly Journal devoted to the Advancement of 
Science, publishing the official notices and pro- 
ceedings of the American Association for 
the Advancement of Science 
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