EXPLANATION OF PLATE XXVIII.

A (x-nicols). Rearrangement by coalesence. White Rock, Australia. (X 114.)

B (x-nicols). Rearrangement by break down of large crystals to small ones. White Rock Australia. (X 114.)

C (x-nicols). Rearrangement of quartz destroying comb structure. Caledonian Mine, Thames, New Zealand. (X 36.)

D (x-nicols). Rearrangement quartz veinlets; individuals growing into silicified wall rock. Cobar, Australia. (X 55.)

E (one nicol) and F (x-nicols). Rearrangement; drusy structure retained by inclusions in quartz entirely unrelated to structure. White Rock, Australia. (X35.)

vein material was deposited. If so, the type of strain indicates the character of the vein: i.e., whether deep-seated or superficial. Brecciation results from unequal pressure, or stress, and though most widespread where there is little load (i.e., near the surface) may be found at any depth at which fissures may exist. Such strain phenomena as the distortion of a crystal without rupture, and recrystallization, however, can only have taken place under the conditions of immense but rather uniform pressure of deepseated deposits. It has been shown that their occurrence is limited to these vein types.

STANFORD UNIVERSITY,
CALIFORNIA.

Talc in its natural condition is a useful mineral. It is soft, sectile, and flexible, but not elastic, and has a decided slippery feel. When homogeneous and compact it may be readily cut to any desired shape and adorned with fine carvings. Being fusible only with difficulty on thin edges, and not affected by ordinary acids, it is stable and indestructible under a wide range of physical and chemical conditions.

Talc contains a small percentage of water which is given off only at red heat. Impurities, especially oxide of iron and silica or grit, depreciate its value. In general the purer the composition and the finer and more homogeneous the structure the higher the grade of talc. When crystalline it is foliated, but

1 Mr. Fairchild made the chemical analyses and Mr. Larsen did the microscopical work. Paper published by permission of the Director of the U. S. Geological Survey.

aggregates of it may vary in structure from very fine, uniformly compact to distinctly granular.

Talc may be applied in the industries either ground, as “talc flour," or unground, as crude talc. Ground talc is most extensively used as a filler in making paper. It is largely employed also in the manufacture of toilet powder, as a filler for paints and lubricants, and for foundry facing, besides many other uses of less importance.

In its crude form talc is most widely employed in the manufacture of pencils or crayons for use on slate or metal, or as French chalk for marking on cloth. In later years it has been used for electric insulators and gas burners, but for these purposes, especially the latter, the United States is deficient in the supply of good material. The object of this paper is to call attention to this lack of supply and to point out certain conditions that have influenced the origin of suitable material, in the hope that domestic production may be increased.

HISTORY.

Although talc was quarried at Göpfersgrün in the Fichtelgebirge and used in Germany as early as 1724 its first application in the manufacture of gas tips in that country was not made until a much later date. Subsequently the work was taken up in the United States, at Cincinnati, by D. M. Steward who used domestic tale first and then that from Germany and India. Some years ago the D. M. Steward Company established its manufactory at Chattanooga, Tenn., and that city has since become an important gas-tip center, as three other manufactories are now operating there. Several other manufactories are located in New York.

PRODUCTION AND IMPORTS.

The production in the United States of talc suitable for gas tips has been limited to North Carolina, Georgia, and Maryland. Much of the material used in 1901 was quarried at Hewitts, N. C. Other localities farther southwest in North Carolina and Georgia were discovered and developed later, and a locality in

Maryland was opened within the last few years. The total output of the grades required for gas burners in recent years has been very small-far from sufficient to supply even the demand of a small industry which in times of peace has depended for its stock of raw material upon imports from Italy, France, Germany, and India. The total amount used annually in the United States for this purpose probably does not exceed 1,000 tons.

The principal sources of imported high-grade talc are Italy and France, which rank first and second respectively in both quantity and quality. Imports from Italy during the last 8 years averaged 4,300 tons valued at $27 a ton, and those from France in the period averaged 2,850 tons valued at $12.50. It is not known how much of these imports from either country is suitable for gas burners.

MODES OF OCCURRENCE.

The most common mode of occurrence of talc used for gas burners, is in metamorphic limestone, but some talc used for this purpose has been found in altered basic igneous rocks.

DOMESTIC DEPOSITS.

Only two domestic deposits have furnished tale for gas burners on a commercial scale. These are at Hewitts, Swain County, N. C., and in Harford County, Md. Other deposits from which samples of high-grade talc have been obtained are found southwest of Hewitts, N. C., especially in the neighborhood of Chatsworth, Ga. The talc in these deposits may be foliated, fibrous, or massive, but only the massive variety can be used for gas tips.

Hewitts, N. C.-Little talc has been produced at Hewitts in recent years. The deposits, owned by the North Carolina Company, occur in large lenses which range up to 50 feet in thickness. and 200 feet in length. These lenses which conform to the bedding of the limestone, stand nearly on edge along the steep slope of the valley and dip steeply to the southeast toward the river. They strike northeastward parallel to the river. Above the river level the lenses of talc have been exhausted, and under the river