iron, calcium or magnesium to form the series of sulphates found in the natural waters. Pyrite and marcasite are very undesirable ingredients of building stone because of their tendency to decompose, whereby the stone itself is disintegrated and discolored through the oxidation of the iron left behind.

E. Oxides.

§ 14. Bog iron ore (limonite).

Before the rich deposits of iron ore were located in the Lake Superior region and Missouri this impure form of iron oxide was eagerly sought. Hubbard in his original survey of the county. located deposits in Secs. 19 and 25, of Summerfield township and called attention to indications in Sec. 3 (T. 9 S., R. 7 E.) of Bedford, and also in London.*

During the present survey other records were obtained of similar deposits. In section 23 of Milan (N. W. 1, S. E. 1) N. D. Baird struck bog ore at a depth of five feet while ditching. It is said to occur also one mile south of Petersburg upon the place of Enos Plomodore (S. W.., N. W. 4. Sec. 10). In the N. W. 1, N. W. 1, Sec. 26 of Bedford, bog ore occurs along a ditch for a distance of ten rods. This mineral occurs in marshes, where it is now forming, and in the beds of former swamps now drained and under cultivation, in beds of varying thickness. Irregular rusty lumps are found in the soil, having a dull earthy luster and without crystalline structure. Their high specific gravity (3.6 to 4) at once distinguishes them from irregular lumps of tufa or clay. The mineral breaks with an irregular fracture, is opaque, can be scratched with difficulty with a knife-point and gives a yellowish brown powder. It is an oxide of iron in combination with water, its formula being 2Fe202+3H2O. When pure it contains 59.8% of iron, 25.7% of oxygen, and 14.5% of water. When mixed with considerable clay it is known as "yellow ochre" and has been used as a paint. Upon the application of sufficient heat the water of crystallization is driven off and the oxide is converted into the red oxide known as hematite (Fe2O2). This also exists in a soft earthy form known as "red ochre," a bed of which three rods square, and one to two feet thick, was located in Sec. 21 of Bedford township, by Hubbard.†

*Second Annual Report State Geologist, 1839, H. R. No. 23, page 112.

The first volume of the American Journal of Science in 1819 announced the "Discovery of American Cinnabar and Native Lead." (pp. 433-4.) A portion of a letter from J. L. Comstock, of Hartford, Connecticut, was published by the editor, which contained an extract from a letter written by B. F. Stickney, Indian Agent

When clay of a brown or yellow color from the presence of the hydrous oxide is burned, as in the manufacture of brick and tile, the conversion to the red oxide takes place in the furnace and a total change in color results. The iron for the formation of beds of bog ore is derived from the soil of the area which is drained into the marsh. It is introduced into the soil from the iron bearing minerals which have contributed to its formation, as hornblende, pyroxene, black mica, pyrite, siderite, etc., of the crystalline rocks. Upon the decomposition of these and other minerals iron is liberated which soon unites with the oxygen of the air forming generally the yellow hydrous oxide. In this form it is abundant in the soil and is insoluble, but must be transported before any beds can be formed. This is accomplished through the agency of decaying organic matter in the soil. The carbon of this organic matter has a stronger affinity for oxygen than has the iron, and some of the oxygen is torn from the iron oxide forming ferrous oxide (FeO). The carbon dioxide (CO2) formed in consequence may unite with the ferrous oxide and form ferrous carbonate (FeCO). This carbonate is somewhat soluble in water containing carbon dioxide and is leached from the soils and transported by the streams to the swamps. Upon standing the carbon dioxide of the carbonate is exchanged for oxygen of the air with the formation of the oxide and the liberation of the CO2. The oxide being insoluble must be precipitated and usually goes down as the hydrous form, that is, the bog ore variety. Beds rarely exceed one to two feet in thickness. From this method of formation it is apparent that the ore will be mixed with sand, clay and other impurities. For this reason and the manner of occurrence this ore has no commercial value at present. Shaler has suggested that as top dressing this ore adds binding qualities. to limestone used in the construction of stone roads.

§ 15. Crystallized quartz.

The Sylvania sandstone has been described as consisting of countless millions of quartz crystals, each a hexagonal prism terminated

at Fort Wayne. The latter says, "I have found a black and garnet colored sand, in great abundance on the shore of Lakes Erie and Michigan, this is sulphuret of mercury, and yields about sixty per cent. It is so easy to be obtained, and is so convenient a form for distillation, that it must become an important article of commerce." In the second volume of the same journal (p. 170) the editor publishes a letter direct from Mr. Stickney, dated "Port Lawrence, Michigan Territory, Mouth of the Miami of the Lakes, June 17th, 1819." in which he says, "From the mouth of the Vermillion, round the whole shore of the western end of Lake Erie, on the shores of the Detroit river, Lakes St. Clair, Huron, and Michigan, the banks are streaked with small reefs of this black and red sand of cinnabar. The whole body of the soil is interspersed with this sand through the whole of this extensive district of country." The editor announced that a sample of the sand, enclosed in a letter had been lost. In his Catalogue of American Minerals, published in Boston, 1825, by Dr. Samuel Robinson this occurrence of cinnabar is noted (page 239). The red and black sand referred to must have consisted of oxides of iron.

by one or two hexagonal pyramids. The formation of these crystals through the secondary enlargement of rounded sand grains has been presented in Chapter III, § 6.

Water saturated with silica (SiO) and standing quietly in fissures and cavities sometimes forms an incrustation of quartz crystals. If no impurities are present the crystals are transparent and without color being known as "rock crystal." Limited quantities of this occur at the Navarre quarries on Plum Creek. When colored purple the quartz is called "amethyst" and this variety was observed at Brest by Dr. Winchell and is reported by Dana as occurring here and at Point aux Peaux and Stony Point. Quartz is readily distinguished from all the other minerals described by its simple physical properties. The form of the crystal is entirely characteristic when this can be made out, the hexagonal prism terminated with the hexagonal pyramid. It has a glassy luster and has no plane cleavage faces, but a conchoidal fracture. Its specific gravity is 2 2-3. It cannot be scratched with a knife or file and scratches glass very easily. It is insoluble in pure water, is unaffected by the ordinary acids and is infusible before the blowpipe. Heated with soda, however, it readily melts and forms glass. It consists, when pure, of 46.7% of silicon and 53.3% of oxygen. § 16. Chert.

This is a variety of uncrystallized or rather cryptocrystalline quartz (SiO2) commonly known as "flint." It is, however, too impure for flint, since it contains a considerable percentage of calcium carbonate. From its resemblance to horn it has been called "hornstone," and owing to its abundance in our Dundee formation gave to it the name of Corniferous (cornu, a horn). As found in Monroe county its color is drab to brown, with a dull to subresinous luster. It is opaque to sub-translucent and is very brittle, breaking with a coarse conchoidal fracture and giving sharp edges. It readily strikes fire with steel and scratches glass with about the same ease as crystallized quartz. Its specific gravity is not perceptibly dif ferent. It occurs in the Monroe beds and the Dundee formation in seams and crevices, in irregular nodules, and as thin beds between the strata of the dolomite and limestone as previously described. In the quarries most of it is seen on the Macon and at Dundee, where it forms thin beds. It frequently encloses fossils in silicified condition, in the cavities of which the silica has some

times crystallized, giving a thin layer of minute crystals suggestive of frost and known as "drusy quartz." The formation of this chert and the origin of its silica have been discussed in Chapter II, § 22. It is too impure for the manufacture of glass, for which flint is used, and its brittleness and lack of binding qualities unfit it for macadamizing purposes. Its hardness, manner of breaking and inertness to the weather made of it a most useful mineral for primitive man. From it he made his spear and arrow-points with which to capture game, the implement with which to prepare, and the spark of fire with which to cook such game. Quarries of a good grade of chert were of more value to him than the richest gold mines of the Klondike or the diamond fields of Kimberly.

F. Phosphates.

§ 17. Apatite.

5

This is a mineral reported by Winchell and Dana as occurring at Brest, Point aux Peaux and Stony Point, but a careful search failed to reveal any of it at the present time. It is a phosphate of calcium, with the formula (CaF) Ca, P3 O12, occurring sometimes in limestones, but more commonly in the crystalline rocks. It contains of P2O, 42.3%, of lime (CaO) 55.5%, and of fluorine 3.8%. When properly prepared it is valuable for fertilizing purposes since it supplies the soil with both lime and phosphorus. Its common mode of occurrence is in the form of elongated hexagonal prisms, of a brown or green color. Its luster varies from glassy to resinous, the mineral looking as though it were slightly oily. It is subtranslucent to opaque, is quite brittle and shows only imperfect cleavage across the prisms. Its specific gravity is a little above the average of rocks (3.2), while its hardness permits of its being scratched, with some difficulty, with a knife-point. It gives no effervescence with the acids. This assemblage of characters readily distinguishes apatite from any other mineral encountered in the county.

§ 18. Asphaltum.

G. Hydrocarbons.

Black, amorphous carbonaceous matter has been mentioned as occurring at various quarries, filling seams and crevices in the dolomites and limestones. Thin layers, more or less continuous,

frequently occur between the beds, rarely attaining a thickness of one-quarter inch. Certain beds at the Woolmith quarry are impregnated with this substance to such an extent that the stone is considerably darkened by it and Mr. G. F. Smith has suggested its use for asphalt pavements, believing that by grinding and heating there would be found sufficient asphaltum to bind together the fragments. As seen in the county, both at the quarries and in the well drillings, the substance is always very impure. If held in a flame it burns for a short time, giving a bright yellow flame and oily odor, but does not perceptibly diminish in bulk. There is usually not sufficient carbonaceous matter present to continue the combustion after the fragment is withdrawn from the flame. When pure, asphaltum is very brittle, of a jet black color and pitchy luster, breaking with a coarse conchoidal fracture. It is soft and very light, its specific gravity ranging from 1 to 1.8. It readily melts and burns with a bright yellow, smoky flame. It is more or less soluble in turpentine, ether and alcohol, but not in water. It has formed where now found by the accumulation of rock oil, which has gradually lost its more fluid constituents and hardened. It is thus of organic origin, has no definite composition, consisting mainly of carbon, hydrogen and oxygen, and cannot be regarded as a true mineral.

§ 19.

H. Key to Minerals.

The following simple key will enable those interested to readily determine the minerals of the county which are encountered in the quarries and well drillings. It will be of no service in identifying the ingredients of the common field boulders. The acid referred to is hydrochloric acid and is prepared by taking a small quantity of commercial strength and adding four times its volume of pure water. In using this a drop of the cold acid is first applied to the solid mineral. If the action is not vigorous the mineral may be reduced to powder at one place and the acid applied, or a fragment may be placed in acid in a test-tube and then heated. After the mineral has been traced, its description, as given in this chapter, should be carefully reviewed for the purpose of verification.