CHAPTER I.

Q. Of what are the rocks composed?

A. According to Geology, soft mud, loose sand, and firm stone, are all called Rock.

Q. How may the rocks be grouped? A. Into three classes: the Igneous rocks, the Aqueous rocks, and the Metamorphic, or altered rocks.

These are again divided into two distinct classes, called the Stratified or Sedimentary rocks, and the Unstratified rocks, and of these the earth's crust is formed.

Q. Which was the first formation of rock.

A. From a state of chaos, when "the earth was without form and void," we have Granite, an Igneous rock cooled down, and forming as it were the framework of the globe.

Q. What are Igneous rocks?

A. Igneous rocks are those formed.

by the action of fire, and were originally in a molten fluid state from the excessive heat.

Igneous rocks which have cooled. down on, or near, the surface of the earth are called Volcanic rocks, and those which have cooled at a depth below it, Plutonic rocks.

Q. What are volcanoes?

A. Volcanoes are mountains from which fire, steam, ashes, stones, and melted lava are discharged, such as Mount Vesuvius, and Mount Etna. There are many other volcanoes in different parts of the world.

Q. Are there volcanoes in the British Isles ?

A. Happily there are no volcanoes in our land at the present time; but Geologists tell us there were such in ages past, long before Man appeared upon the earth.

Snowdon, in Wales, is an old volcano. Staffa, and many islands of the Hebrides, are said to be fragments of lava streams. Edinburgh Castle

is built on the cone of an extinct volcano.

Q. What are Aqueous rocks?

A. Aqueous rocks are those formed by deposits of mud, sand, lime, shells, etc., at the bottom of the sea, through the action of water.

These materials are usually arranged in tolerably regular strata, or layers, and are therefore called Stratified rocks.

Igneous rocks, on the contrary, are not laid in beds or layers, but in irregular masses forced up from below, and are therefore called Unstratified rocks.

Q. How has the sediment of Aqueous rocks become hard like stone?

A. By time and pressure, as layer after layer settled down one over the other. Or it may be a solution of lime or iron, or some mineral substance acted as a cement upon it.

Q. What is the third division of rocks?

A. It consists of rocks, which,

though stratified, have been much changed since their first deposits, chiefly by heat, pressure, and water. These are called Me-ta-mor-phic or altered rocks.

Of these three divisions of rocks all the others have been formed, by the different varieties passing into one another, as well as by the single or combined influences of heat and water. Q. What are Aerial rocks?

A. Aerial rocks are so named because they have accumulated in the open air, such as hills of blown sand, and heaps of stones that have fallen at the bottom of precipices.

Q. What are Organic rocks?

A. A class of rock usually included in the Aqueous rocks, consisting almost wholly of the remains of plants and animals. Being thus principally composed of organisms, they are often called organically-formed rocks.

The crust of the earth, so far as it can be examined, is chiefly made up of Sedimentary and Organic rocks.