FOURTH CLASS. Superincumbent Rocks include those hornblende rocks which lie over other rocks, in a non-conformable position; they are considered by many geologists as of volcanic origin. These rocks are, Amygdaloid, or Basalt, and Greenstone Trap. Amygdaloid is an aggregate of hornblende particles; colour is dark gray, or brown. Greenstone Trap is an aggregate of hornblende and feldspar. This rock forms the Palisadoes, on the Hudson River. FIFTH CLASS. Alluvial includes deposites which are made of broken strata, consisting of clay, sand, and pebbles. This class is divided into three sections, viz. : Antediluvial, before the flood; Diluvial, at the flood; and Postdiluvial, after the flood. Plastic Clay, of a white, or gray colour: it contains some siliceous, but no calcareous matter; it contains gypsum and fullers' earth. Marly Clay consists of a stiff blue, or blackish clay, and calcareous matter it is found on the banks of the Hudson, at Albany. Bagshot Sand consists of loose porous sand, of a brown colour. The barren soil on the banks of the Hudson River is mostly composed of this sand. It is recommended to the teachers of this book, to procure a small cabinet of minerals. The whole number of specimens which form a complete system of Geology is only about thirty, and so common, as to be easily obtained. The numerous cities found upon the globe may be divided into 12 classes, according to their population. In the following table will be found the population of each class of cities, with examples. The same classes are used for the population of islands also. Population. Class. I. 1,000,000 and above, Example. Paris. (Eur.) III. 300,000 to 500,000 IV. 200,000 to 300,000 Naples. (Eur.) V. VI. 150,000 to 200,000 N. York & Philad. (U. S.) 150,000 Liverpool, (Eur.) 90,000 Genoa. (Eur.) 70,000 Baltimore. (U. S.) 50,000 Boston. (U. S.) Charleston. (U. S.) 30,000 Geneva. (Eur.) XII. 10,000 to 20,000 { Richmond, &c. (U. S.) Albany, Providence, LARGE TOWNS, above 5000 Hartford. (U. S.) SMALL TOWNS, under 5000 Page ERRATA TO MODERN GEOGRAPHY. 16, 25th line from top, for in their connection, read and their con 56, in the 4th class of Rivers, for Vermeyo read Vermejo. for Onion R. read Onion Vt. 63, 19th line from top, for visiters read visiter. 85, bottom line, insert the before the word Mississippi. 105, 3d line from bottom, for low read long. 133, Opposite Rome in the table, for 1798 ft. read 1978 ft. insert Geneva of a College recently established. 280, Table, opposite British Islands, for 776,500 read 726,000. 282, 13th line from top, after rugged tracts insert as some of the neigh |