Now, all this may be summed up in the one word "transportation;" and we shall presently inquire how the rocky matter of which the mountains are built was transported.

Secondly. We have to inquire how the bricks and stones were raised up. The analogy is not quite perfect in this case; for the mountains were raised up en bloc, not bit by bit and stone by stone, as in the case of the cathedral. Still they have been raised somehow. Analogies are seldom complete in every detail; but for all that, our illustration serves well enough, and will help us in following the various processes of mountain building. In these days, the raising of the stones is mostly effected by steam-power applied to big cranes and pulleys. In old days they used cranes and pulleys, but the ropes were pulled by hand-power. In either case the work proceeds slowly; and we can easily picture to ourselves the daily raising of the stones of which the cathedral is composed. "What were the forces at work which slowly raised the mountains?" This question we will endeavour to answer later on (see [next chapter]). This work may be included in the one word, "elevation."

And lastly. We must inquire how the carving of the stately building was effected, how its pinnacles received their shape, and how all those lovely details received their final forms; how the intricate traceries of its windows were made, and the statues carved which adorn its solemn portals. This question is easily answered, for we are all more or less familiar with what goes on in a stone-mason's yard. Under those wooden sheds we see a number of skilled labourers at work, busy with their chisels and mallets, cutting out, according to the patterns made from the architect's detailed drawings, the portions of tracery for windows, or the finials, crockets, and other features of the future building. In another part of the yard may be seen the stone-cutters, working in pairs and slowly pulling backwards and forwards those long saws which, with the help of water and sand, in time cut through the biggest blocks. All this work then may be summed up under the one word, "ornamentation," for it includes the cutting and carving of the stone.

Our three lines of inquiry may now be summed up in these three words, which are easily remembered:—

Taking the first of these subjects for consideration in the present chapter, we have now to inquire into the nature of the materials of which mountains are composed and the means by which they have been brought together and compacted into hard rock.

First, with regard to the nature of the materials which Mother Earth uses to build her rocky ramparts: they are the same as the ordinary rocks of which the earth's crust is composed; and the greater part of them have been formed by the action of water. These are the ordinary "stratified" rocks, which in one form or another meet us almost everywhere, and may be said to be aqueous deposits, or sediments formed in seas and inland lakes. They are always arranged in layers, known to geologists as "strata," because they have been gently laid down, or strewn (Latin, stratum), at the bottom of some large body of water. There were pauses in the deposition of the materials, during which each layer had time to harden a little before the next one was formed. This accounts for the stratification. In this way great deposits of sandstone, clay, and limestone, with their numerous varieties, have been in the course of ages gradually piled up, till they have attained to enormous thickness, which at first sight seem almost incredible; but the bed of the seas in which they formed was probably undergoing a slow sinking process that kept pace with the growth of these deposits, otherwise the sea might have been more or less filled up.

And these processes are still going on. In fact, it is entirely by watching what goes on now that geologists are able to explain what took place a very long time ago when there were no human beings on the earth to record the events that took place. And so we argue from the present to the past, from the known to the unknown. In other words, geology is based upon physical geography, which tells us of the changes now in progress on the earth. Thus, sandstone, as frequently met with in different parts of Great Britain, and largely used for building purposes, such as the familiar old red sandstone[20] of South Wales, Hereford, and the north of England and different parts of Scotland, was once soft sand in no way at all different from the sand of the seashore at the present day, or of the sandy bed of the North Sea. In process of time it became hardened, and acquired its characteristic red colour, which is due to oxide of iron. In some places numerous fossil fishes have been discovered in this interesting formation, so intimately associated with the name of Hugh Miller, who first thoroughly explored it; these and other remains entombed therein tell us of the strange forms of life which flourished on the earth during that very old-fashioned period of the world's history; and by putting together all kinds of evidences derived from the rock itself, geologists are able to form a very good idea of the way in which this rock-deposit was accumulated, always, however, basing their conclusions on a thorough knowledge of what goes on at the present day in seas, rivers, and inland lakes.

In the great series of stratified rocks forming what is commonly called the crust of the earth (an unfortunate term which has survived from the time when the interior of the earth was generally believed to be in a fiery molten condition, and covered by a thin coating of solid rock at the surface), there are besides the sandstones, of which we have just spoken, great deposits of dark-coloured clays, shales, and slates. All these can be accounted for by the geologist. They are simply different states of what was once soft mud. The slates tell us that they have been subjected to very severe pressure, which squeezed their particles till they were elongated and all arranged in one direction, and this is the reason why they split up into thin sheets.

Others, again, represent vast deposits of carbonate of lime, thousands of feet thick and now occupying hundreds of square miles of the earth's surface. Limestone rocks are as abundant in our own country as the sandstones, shales, or slates. The chalk of which the North and South Downs are composed is a familiar example. It is seen again forming Salisbury Plain, in Hampshire and the Isle of Wight, and then it may be traced running up the country in a long band through the counties of Oxford, Cambridge, Lincoln, until it reaches the coast at Flamborough Head in Yorkshire. Then we have the Bath Oölites so much used in building, for they form an admirable "freestone" that can be easily carved and cut in any direction (hence the term "freestone"); and lastly, the great mountain limestone so well developed in South Wales, Yorkshire, and the Lake country. All these were slowly built up at the bottom of the seas which existed in past ages; great beds of gravel formed at the mouths of rivers, and long banks of pebbles and rounded stones collected on the shore of primeval seas, and were ground against each other as now by the action of the waves, until all their corners were rubbed off. Pebble-beds, called by geologists conglomerates, are met with among the stratified rocks; and their story is easily read by studying what takes place at the present day on our seashores.