CHAPTER VII.. Soils of the Granitic and Trap Rocks.—Accumulations

Soils of the Granitic and Trap Rocks.—Accumulations of transported Sands, Gravels, and Clays.—Use of Geological Maps in reference to Agriculture. —Physical characters and Chemical constitution of Soils.—Relation between the nature of the Soil and the kind of Plants that naturally grow upon it.

It was stated, in the preceding lecture, (see p. 82,) that rocks are divided by geologists into the stratified and the unstratified. The stratified rocks cover by far the largest portion of the globe, and thus form a variety of soils, of which a general description has just been given. The unstratified rocks are of two kinds—the granites and the trap rocks; and as a considerable portion of the area of our island is covered by them, it will be proper shortly to consider the peculiar characters of each, and the differences of the soils produced from them.

The unstratified are often called crystalline rocks, because they frequently have a glassy appearance, or contain regular crystals of certain mineral substances; often also igneous rocks, because they appear all to have been originally in a melted state, or to have been produced by fire.