streets were planked. In 1855 1.72 miles of actual pavement was laid, but of what material the reports do not state.

San Francisco. In the big fire that occurred in San Francisco in 1850, many planked streets were set on fire and consumed.

Roads constructed for short distances of natural asphalt in southern California had been known for a long time prior to 1870.

New Orleans. New Orleans constructed her first pavements of cobblestones in 1817, when the population of the city was about 41,000. Previous to this time it had not been deemed practicable to lay a pavement successfully on the soft yielding soil of the city. A general paving ordinance was passed in 1822, and under its provisions streets were improved with shells, cobble, square blocks, and irregular flat stones.

In 1837 an ordinance ordered certain streets paved with the "gunnels" of flat boats, although they had been used previous to that time.

In 1838 a portion of St. Charles Street was paved one-third with stone blocks, one-third with curbstones laid flat, and one-third with hexagonal pine blocks. The stone and wood blocks were satisfactory, and their use was continued.

A bituminous pavement of some kind was laid on Gravier Street in 1880, but proved a failure. Asphalt was first laid on St. Charles Street in 1885.

From 1889 to 1896 a number of streets were paved with gravel concrete, but the material did not give good satisfaction.

Brick was used in 1894, and chert in 1895.

The dimensions of granite blocks were 14 × 10 × 88 inches. Cleveland. The first stone pavements of Cleveland were constructed between 1851 and 1854, of Independence sandstone. The blocks had a surface of 8 or 10 by 12 inches and were from 8 to 12 inches deep.

Medina sandstone was first used in 1856, and the streets then paved were in good condition in 1880.

Nicholson pavement was laid in 1866. In 1873 an experiment was tried by laying a mixture of coal-tar and roofing-gravel to a depth of three inches on six inches of broken stone. The results were not good.

St. Louis. Main Street in St. Louis was paved with stone in 1818. The blocks were roughly dressed, irregular in shape, from 3 to 12 inches thick, 6 to 14 inches long, and 6 to 10 inches deep, and set on 6 inches of sand. In 1842 the specifications called for a regular block 4 to 5 inches thick, 7 to 12 inches long, and 10 inches deep, set on 7 inches of gravel.

Macadam was adopted in 1832.

Wood has been experimented with in St. Louis to a great extent. In 1851 and 1852 many streets were planked. In 1867 Burnettized cottonwood was used. This pavement lasted about seven years, when it was replaced with untreated pine, which had about the same life.

use.

Cobblestones were tried in 1855, but never came into general

Granite and asphalt blocks were adopted in 1873, and sheet asphalt in 1883.

Albany. In September, 1704, the City Council passed the following resolution: "It is also ordered that ye streets be paved before each inhabitant's door within this citty, eight foot breadth from their houses and lotts before ye 25th of October next ensueing, upon penalty of forfeiting the summe of 15s. for ye behoofe of ye Sheriffe, who is to sue for ye same."

In connection with the visit of Peter Kalm in 1749 it is stated that "the streets are broad and some of them are paved." In 1764 it appears from Mrs. Grant's "Memoirs of an American Lady" that State Street was only paved on each side, the middle. being occupied with public edifices. Active paving work was not. begun till about 1791, when Broadway was paved and complaint was made about the quantity of stones required, as "it swallowed up thousands of cartloads." Cobblestones were the only material used for years, dimension granite blocks having been not adopted until 1873.

CHAPTER II.

STONE.

THE rocks that once formed the crust of the earth were composed almost entirely of nine elements, oxygen, silicon, magnesium, aluminum, calcium, iron, sodium, potassium, and carbon, the whole making 97.7 per cent of the earth's crust.

These elements combining in different ways formed minerals, and these minerals make the different rocks according to the number and quantity of their components.

Rock can be defined as any material forming a portion of the earth, whether hard or soft. Rocks are divided into two general classes, stratified and unstratified. Stratified rocks are more or less consolidated sediments and are of aqueous origin. Unstratified rocks, having been more or less completely fused, are crystalline in form and of igneous origin.

The igneous rocks, while not all granite in the strictest sense, may be called granitic, for they are granular and made up generally of the same substances as the granites, varying in their proportions and structure.

The minerals forming these rocks are generally considered as being divided into essential parts and characterizing and microscopic accessories. These terms are self-explanatory, the essential parts making up the body of the stone, the characterizing accessory defining its exact variety, and the microscopic being those contained in very minute quantities.

The important minerals that make up these rocks are quartz, feldspar, amphibole, pyroxene, and mica.

Quartz.

Quartz is a pure silica, composed of silicon and oxygen; its specific gravity is 2.65 and it is a hard and brittle mineral. It is

always found of the same composition and hardness, although the shape of its particles varies considerably. It is practically indestructible by the forces of nature, which accounts for its forming so large a proportion of all sands. Those found on the seashore are nearly all quartz. When absolutely pure, quartz is colorless, but sometimes it contains impurities enough to give it a color, when it is known as rose quartz, smoky quartz, etc., according to its appearance. When it is in a metamorphic state with its crystals cemented together with quartz, it forms a rock called quartzite.

Feldspar.

Feldspar is an anhydrous silicate of alumina together with soda, potash, or lime. It is generally softer than quartz, with a specific gravity of from 2.4 to 2.6. There are several varieties of feldspar; the principal ones being orthoclase, microcline, albite, oligoclase, and labradorite. It is also divided into two groups according to its crystallization, the monoclinic and the triclinic. The former contains principally silica, alumina, and potash; the latter with the exception of microcline, which chemically is almost the same as the monoclinics, has no potash, but in its stead sodium and lime. According as the above constituents vary in quality and quantity, the feldspars vary in hardness and color, and when they are in appreciable quantities they have an important bearing on the resulting rock. It is susceptible to the action of the elements, all clays being formed by the decomposition of feldspar.

Amphibole.

This mineral is sometimes called hornblende, which term really belongs to but one variety, of which there are two, the aluminous and the non-aluminous. The former contains about 45 per cent of silica, 17 of magnesia, 10 of alumina, 12 of lime, and 16 of iron oxides; the latter 57 per cent of silica, 26 of manganese, 14 of lime, with small amounts of oxide of iron and manganese. Hornblende belongs to the aluminous variety. Hornblende is hard and tough and imparts these characteristics to all rocks of which it becomes a part. It is found in some metamorphic rocks. Its color is generally a brownish green.

Pyroxene.

Pyroxene is more brittle than hornblende and consequently not so desirable a constituent for a rock. Its principal variety, augite, is an essential ingredient of diabase and basalt and also an accessory. It is dark-colored and composed approximately of silica 50 per cent, alumina 6 per cent, magnesia 15 per cent, lime 23 per cent, and iron oxides 6 per cent.

Mica.

This is the mineral so well and popularly known as isinglass. There are several varieties, but the two found in granite rocks are , muscovite and biotite. They are always found in thin sheetlike forms and are important factors in the make-up of rock, both as to color and structure. They are influential disintegrating agents, as, on account of their laminations, they often allow the entrance of moisture, which is an important element of decay in any material. If the mica is deposited in different layers or planes, the rock readily splits along these planes. If muscovite is the variety present, the rock is generally light-colored, while the black biotite imparts its color to the stone, often giving it a speckled appearance. Muscovite is a silicate of potash and alumina, and biotite of alumina, iron, and magnesia.

Having somewhat hastily examined these mineral constituents of the granite rocks, it will now be in order to take up the rocks themselves. They are complex in their composition and structure, having been formed at different times and under different conditions; some containing but few and others many minerals, often grading into each other so imperceptibly that it is sometimes almost impossible to determine where one variety ends and the other begins. For this reason, and on account of the different definitions given to the same variety by equally good authorities, it seems proper to treat these rocks as one class, each according to its characteristics, and not attempt to make any arbitrary class distinctions.

The group of rocks which it is proposed to study in this connection may be defined as silicious, holocrystalline, granular rocks. Their essential constituents are quartz and feldspar, and the characterizing accessories hornblende, pyroxene, and mica, with some