seen the manufacture of lime. This is also carried on at Rockport and Thomaston. The Rockland limestone has a higher percentage of calcium than any other considerable deposit in the country, and is reputed in the building market to make the strongest mortar. The quality and quantity have been materially improved by the introduction of patent kilns, in 1850, and the more recent introduction of coal as fuel. In 1890 a steam railroad was constructed to transport the stone from the quarries in the rear of the town to the kilns on the water front. Formerly in the hands of independent operators, the industry passed over to the Rockland-Rockport Lime Co., which now controls the railroad and about three-fourths of the product. The company also operates a large factory for the manufacture of hydrated lime. The shipments to New York and other points are largely made in barges towed by tugs. The granite business is important. Two of the largest granite companies of the country have quarries in the vicinity, on the islands and on the mainland. These companies have handled some of the largest stones that have ever been wrought. The United States custom house in St. Louis, the postoffices in New York and Cincinnati,' and many of the largest and handsomest buildings in the country have been built of Rockland granite. Steam and gasoline engines and blacksmiths' and granite workers' tools are manufactured. Fishing is carried on to some extent. Clams and sardines are canned, and more than 2,000,000 pounds of lobsters are shipped annually from here by rail. It is an important distributing point to the towns of eastern Maine.

The public buildings are the U. S. custom house and postoffice building, which is a handsome granite structure and cost about $150,000, and the County court house and jail, which are of brick with granite trimmings and are on the same lot. The two cost something more than $100,000. There are many handsome residences with fine grounds. In one of the cemeteries is a statue of white Italian marble of General Hiram G. Berry, who was a citizen of Rockland, and was killed at the Battle of Chancellorsville. It is the work of Franklin Simmons. Pop. (1910) 8,174.

LEWIS FREDERICK STARRETT.

Rockland, Mass., town in Plymouth County; on the New York, New Haven and Hartford railway; about 17 miles south by east of Boston. Until its incorporation as a separate town in 1874, it was a part of the town of Abington of the old Plymouth Colony. The town is pleasantly situated and its proximity to Boston and the convenience of transportation, give it an excellent trade and have made it a popular suburb of that city.

Rockland is a manufacturing place of grow ing importance. The census of 1900 returned 81 establishments with a combined capital of $998,824, employing 1,071 persons at $515,974 in annual wages. They used $1.363.959 in materials and had a product valued at $2,288,972. The industry first in importance was the manufacture of boots and shoes. Tacks are also extensively manufactured; and other factories

produce heels and shoe-findings, box board, shos boxes, and soaps.

Rockland has well-built factory and public buildings, churches, schools, and attractive homes. It has two banks, a public library, and weekly newspapers. Pop. (1890) 5,213; (1900) 8,150; (1910) 6,928.

Rockland, N. Y., a county in the southeastern part, bordering on New Jersey, and bounded on the east by the broadened expanse of the Hudson River known as the Tappan Zee and Haverstraw Bay. Nyack (q.v.), its largest town, is about 30 miles from New York, and in the vicinity, which is near the northern end of the Palisades of the Hudson and rugged and picturesque, are many handsome estates of New City. The county is served by the New York, York business men. The county-seat is New L. E. & W., the New Jersey & N. Y., and the West Shore R.R.'s; and while in many parts the soil is rocky, has, particularly in the eastern part, rich farms and large dairy interests. In the western section are the Ramapo Mountains, which contain the sources of the Ramapo and Hackensack Rivers. Granite, gneiss, limestone, trap, and red sandstone are extensively quarried, the last a good building-stone; the brick manufactories are important; and large quantities of fruit, green vegetables, butter, and milk are shipped daily to New York. Many of the farmers "take boarders" during the summer months, and its healthfulness and its proximity to the city make Rockland County a popular vacation resort.

Rockland Lake, N. Y., a village of Rockland County, on the West Shore Railway, and on the Hudson River; four miles above Nyack and 30 miles above New York. It has only a small permanent population but is a Lake, a large sheet of clear, fresh water, from popular vacation resort, Near here is Rockland which 300,000 tons of ice are taken annually for use in New York.

Rockling, a European fish of the cod family and of the genus Motella, three species of which are regarded as valuable in British markets.

Rockport, rok'port, Ind., city, county-seat of Spencer County; on the Ohio River, and on the Louisville, E. & St. L. railroad; about 100 miles southwest of Louisville, Ky., and 30 miles in direct line east by south of Evansville. It has steamer connections with all the river ports. It is on a bluff about 100 feet above high water. It is in an agricultural region in which grain and tobacco are the chief productions. The city has considerable manufacturing interests; the principal industrial establishments are flour and grist mills, foundry, machine shops, tobacco stemmeries, brick works, basket factories, creamery, wagon and carriage works, and furniture factories. It has a library founded in 1855. Pop. (1890) 2,314; (1900) 2,882; (1910) 2,736.

Rockport, Mass., town in Essex County; on the Atlantic Ocean, and on the Boston & M. railroad; about 30 miles northeast of Boston.

it is on an island, the same on which Gloucester (q.v.) is located. The town embraces several villages. Electric lines connect Rockport and Gloucester and many points on the island. It was settled in 1690 by Richard Tarr and was known at first by the name "Sandy Bay." It is a famous summer resort; near Pigeon Cove, one of the villages, are a number of summer cottages. Part of the land is fertile and is used mainly for market gardening. Some of the places of interest in the vicinity are Dogtown Commons, where in the last of the 18th century a hundred families exiled themselves and lived in loneliness and poverty on those boulder strewn hills. Their numerous dogs gave the place its name. Other places of interest are Doctor's Run, The Headlands, and the Straitsmouth Life Saving Station at Gap Cove. In the northeastern part of the town are extensive granite quarries. The Boston post-office is built of granite obtained from these quarries. The chief manufacturing establishment is an isinglass factory which employs about 1,000 persons. There is one national and one savings bank. There are 12 churches, and the educational institutions are a high school, grammar and primary schools, and a public library, opened in 1871. Pop. (1910) 4,211.

G. M. HASKINS.

Rockport, Texas, town, county-seat of Aransas County; on the Aransas Bay, an inlet of the Gulf of Mexico, and on the San Antonio & A. P. railroad; about 170 miles southwest of Galveston, and 135 miles south by east of San Antonio. It was settled in 1865 by Doughty and Mathis; was incorporated in 1865 and chartered as a city in 1871. It has steamer connections with all of the Gulf ports. It is on the peninsula, Live Oak Point; and the cool gulf breezes make it a popular summer resort. It has extensive fishing interests, especially oysters, and small game is plentiful in the vicinity. Rockport makes large shipments of hides, livestock, and fruit. There are five churches, a high school, elementary schools, and one national bank. The government is vested in a mayor and a board of aldermen, eight in number, who are elected biennially. Pop. (1900) 1,153; (1910) 1,297. C. W. NEWMAN, Editor Enterprise.'

Rocks. Regarded as a whole, the earth, so far as we can examine it first hand and thus know it intimately, consists of three envelopes: (1) an outer gaseous envelope called the atmosphere; (2) a middle aqueous envelope called the hydrosphere; (3) an inner solid envelope called the lithosphere. These envelopes, considered together, including the lithosphere to a depth of 10 miles below the sea-level, have been shown to consist quantitatively of the following elementary substances:

The above-named elements, so far as they enter into the composition of the lithosphere, rarely occur in the uncombined state, but are usually united chemically in different proportions to form those more or less definite chemical compounds called minerals (for example, quartz, SiO2; calcite, CaO.COz; olivine, (MgFe),SiO.); and minerals in turn are aggre gated in various ways to form rocks. A rock may be defined as any accumulation or aggrega, tion of one or more mineral species or substances, potential or actual, which constitutes a considerable component of the lithosphere; for example, granite, sandstone, limestone, clay, gravel, salt-beds. Although the crest of the earth or lithosphere has been shown to contain many hundreds of species of minerals, nevertheless the great bulk of it is composed of comparatively few species, and these have been termed the rock-forming minerals, in contradistinction to the great multitude of mineral species found more particularly in veins, and which, though of great importance economically, and of primary interest scientifically, are insignificant in amount when compared with the, great mass of the more common minerals which go to make up a large portion of the earth. Thus gold, silver, platinum, the sulphide ores, and the minerals containing such rare substances as thorium, uranium, or radium, are negligible in quantity when compared with the mass of minerals composing the lithosphere.

The science or treatise of rocks, in its broadest scope, which considers them in all their relations, is called petrology or lithology, while the systematic and descriptive science of rocks, leading more particularly to their nomenclature, is called petrography. This distinction is implied in the etymology of the words. The latter term is used commonly in connection with the microscopic study of the igneous rocks.

Those minerals which are of especial importance as rock-formers can be grouped as follows:

GROUP I.

Quartz. This group, for present purposes, may be limited to a single species, quartz, which is one of the most abundant of minerals, and is remarkable otherwise for its rather superior hardness, lack of cleavage, and indestructibility. It has strong crystallizing powers and, where allowed to grow intact, forms those beautiful hexagonal crystals with which all are familiar. Chemically it is an oxide of silicon, SiO2, that most abundant of all acid radicals, which, when combined with the bases alumina, lime, iron, magnesia, and the alkalies, soda and potash, in different ways, forms that most important of all classes of mineral substances, the silicates.

GROUP II.

Feldspars. These are the most abundant of all rock-formers. They comprise a rather complex group of silicates, where alumina, the alkalies, potash and soda, and the alkaline, earthlime, are the bases. On a chemical and crystallographic basis they fall naturally into two series, the orthoclase and the plagioclase. Orthoclase, so called because of the rectangular cleavages lying parallel to the ortho- and clinopinacoids, is the type-species of the series. It is a silicate of potash and alumina having the chemical composition KAlSi,Os, and is otherwise

known as potash feldspar. It belongs to the monoclinic system of crystallization, and is further known as the monoclinic feldspar. A part of the potash of orthoclase may be replaced by soda. In fact most of the analyses of the mineral show one per cent or more of the substance. This replacement of potash by soda can take place until these two constituents are present in nearly equal proportions without altering the monoclinic character of the species. Such an orthoclase is called soda-orthoclase. Sodaorthoclase has a chemical composition represented by the formula (Na,K) AlSiOs, where soda predominates over potash. Under the microscope and between crossed nicols it exhibits a peculiar patchy appearance easily recognized.

Mocrocline, like soda-orthoclase, contains both potash and soda, (K,Na) AlSi2O8. It is, however, triclinic, but only slightly so, as the cleavage angle between the pinacoids varies but slightly from 90° (89° 30′), hence the name. Between crossed nicols it exhibits a peculiar cross-hatching, due to multiple twinning according to both the pericline and albite laws, and is thus usually easily distinguished under the microscope. It stands at the head of the true plagioclase series, but inasmuch as it possesses a notable amount of potash, it may be classified with soda-orthoclase as representing the transition varieties of feldspar, lying between the monoclinic, potash, orthoclase series and the triclinic, soda-lime, plagioclase series.

The more typical plagioclases are represented by albite, oligoclase, andesine, labradorite, bytownite, and anorthite, which together constitute the albite-anorthite series. The theory of their constitution was propounded by Tschermark in 1864. He showed that the series can best be explained as a mixture of two extreme molecules, the one a pure soda-alumina silicate molecule, and the other a lime-alumina silicate molecule, found in anorthite. The intermediate varieties can be considered as varying mixtures of these two molecules. Representing the albite molecule by Ab and the anorthite molecule by An, the series is expressed thus:

This series of mineral varieties furnishes one of the best illustrations of an isomorphous mixture. It constitutes the albite-anorthite or sodalime series of plagioclase feldspars, all of which are distinctly triclinic. The cleavage angle in this series varies from 93° 31′ in labradorite to 94° 5' in albite.

Usually the plagioclase feldspars can be quickly and surely distinguished from the microcline or the orthoclase varieties by their characteristic multiple twinning, which is manifested in thin sections between crossed nicols by a distinct parallel banding that traverses the individual mineral plates. It thus becomes a comparatively simple matter, with thin sections under the microscope and between crossed nicols, to distinguish between orthoclase, which normally shows plain non-striated plates, sodaorthoclase, which has a peculiar patchy appear

ance, microcline with its more or less indistinct cross-hatching, and plagioclase with its characteristic, sharply defined, parallel banding. Furthermore, the different varieties of the plagioclase series can be identified by their behavior in polarized light, more particularly by the variation in their extinction angles. In a general way this angle may be said to increase in size in passing from the albite toward the anorthite end of the series.

The feldspars are not only of primary importance as rock-formers, but the classification of rocks as at present accepted (more particularly the igneous varieties) depends largely upon the kind of feldspar which they contain.

The feldspars can be grouped in tabular form thus:

Crystallizing as they do in two systems, the feldspars are said to be dimorphous; and the group may be described as consisting of a series of isodimorphous mixtures of the orthoclase albite and anorthite molecules.

Frequent parallel intergrowths of two varieties of feldspar occur; for example, albite may be intergrown with microcline or orthoclase, where the albite shows as bands of a different-colored mineral matter runnarrow irregular ning across the cleavage surfaces of the orthoclase or microcline. Such intergrowths are called perthitic intergrowths or perthite because certain flesh-red feldspars from Perth, Canada, were first shown to be made up of such intergrowths. These intergrowths are sometimes so minute as only to be made out with the microscope, and then they are called microperthite. Brögger has suggested that certain soda-orthoclases are intergrowths of this kind in which the albite lamellæ are so narrow as not to be discoverable even with the highest powers of the microscope. For these supposed intergrowths he proposes the name cryptoperthite.

Similar parallel intergrowths of distinct mineral species may occur where quartz is intergrown with microcline. Such intergrowths of quartz and feldspar (usually orthoclase or microcline) are common in certain granite-like rocks called pegmatite, and are known as pegmatitic intergrowths, or graphic granite, referring to the resemblance of the curious V-shaped areas of quartz to cuneiform writing.

GROUP III.

Feldspathoids.-The minerals of this group are called feldspathoids or feldspar-like minerals, more particularly because of their chemical resemblance to the feldspars. There are but two species which need be considered here: leucite, which has a chemical composition expressed by the formula KAI (SiO2)2; and ne