CHAPTER V.

THE STORY OF A PIECE OF SANDSTONE.

"You may trace him oft

By scars which his activity has left

Besides our roads and path-ways (though, thank heaven,
This covert nook reports not of his hand),

He who with pocket-hammer smites the edge
Of every luckless rock or stone that stands
Before his sight by weather stains disguised,
Or crusted o'er with vegetation thin,
Nature's first growth, detaching by the stroke
A chip or splinter-to resolve his doubts;
And with that ready answer satisfied,

Doth to the substance give some barbarous name,
Then hurries on; or from the fragment, picks
His specimen."

WORDSWORTH's Excursion.

IKE my mineralogical acquaintance, the piece of limestone, generally I am about to do duty for a group of individuals.

common to every geological formation. But each of us has a separate story to tell, and I shall find it quite sufficient to bring all the circumstances of the epoch in which I lived sufficiently clear to my own recollection. It is said that a number of people who live in the present period (so far removed in time from mine) profess to be

able to interrogate a piece of limestone or sandstone, by what they term Psychometry, and to get its story in some easier way than by the ordinary cross-questioning of science! All I can say is, I wish the events of my own life were so permeated in my substance. If this theory be true, the modern science of geology will have to give up induction, and fling itself into the arms of the spiritrappers!

Every one of my listeners knows what a piece of sandstone is like. There is no need for me to describe my appearance, therefore, as novelists do their heroes. But how many thus familiar are aware that in ninety-nine cases out of a hundred every such piece of sandstone was originally formed along the floor of ancient oceans? Those ocean bottoms are now represented by dry land surfaces, where the vegetation luxuriates on the mineral substances accumulated under such widely different circumstances. Even where no marine organic remains are present, as fossils, to prove the marine origin of the sandstones, that origin is none the less certain. I cannot speak with certainty as to the nature and extent of the dry lands and continents of the epoch in which I was born. Suffice it to say, they must have been great, for the rivers which watered them were large, and brought great quantities of mud and sand down to the sea. The ocean currents and tides also wore away the coast-line, and added to the quantity of loose sand and mud which accumulated

under the waves in consequence.

I was born.

Thus it was that

My earliest remembrances are of my lying loose and unconsolidated on the ocean-floor, and of constant additions being made to the sheet of which I formed part. It was whilst I was lying in this state, as so much ordinary sand, that I received my impressions of what was going on around me. These consisted of a familiarity with the commoner

Fig. 18.

Culceola sandalina.

animals which lived in the sea, or with occasional plants and vegetables which had been carried there by rivers, until they sank to rest in my bosom when they had arrived at a water-logged condition. Of these I will speak presently. Meantime let me make a few remarks as to the changes which transposed me from loose marine sand into hard sandstone; and in doing so,

it will be evident that the same explanations will answer for the similar alteration of sandstone rocks, both of earlier and later geological periods.

The sand or mud brought down and laid on the sea-floor in the manner I have mentioned was not of an absolutely pure character as regards its mineral composition, that is to say, it was not all silica, or alumina, as the case might be. In most

instances the material was mixed with more or less of iron rust, or of lime, and silica. The two latter acted as cementing pastes to those sandstone rocks which are now of a lightish colour; whilst the iron was the compacting agent with such dark red rocks as that of which I form part. Indeed, in most cases, even when the sandstone is of a light yellow, a small percentage of iron has gone a great way towards binding the loose grains of sand together, and thus producing a hard rock. When this chemical agent has been equally dispersed through the sandy mass, you have the thick-bedded sandstone, or "free stone." When it was intermittent in its action, or unduly mixed up, or occasionally alternated with something else, then the sandstone becomes "flag-stones" of greater or less thickness.

Sometimes you will see a mass of red sandstone more or less mottled. This has been caused, in most instances, by patches of vegetable matter— old world fucoids or something of that sort,-which decomposed, and whose chemical changes combined with the iron, and locally prevented its colouring effect.

Of course it will be evident that our hardness or softness greatly depends on the percentage of cementing material, or to the different circumstances under which we were formed. I have doubt that, when the chemical changes above mentioned were going on through an immense thickness of accumulated sand, the hardening process was

no

greatly assisted by the pressure of the overlying volume of sea-water.

The epoch to which I belong is sometimes called the "Old Red Sandstone," and, occasionally, the "Devonian." The former term is given to our formation to distinguish us from the "New Red Sandstone," overlying the coal-measures; whilst the latter name is of local origin, and indicates that the system is largely developed in the lovely county of

Devon. Indeed, that sunny land owes no little of its physical attractions to the various mineralogical structure of the rocks of our formation. Perhaps I can boast of the fact that there are few other formations which have such a world-wide extent as that to which I belong. In the United States. it stretches over an area nearly as large as Europe, there being one continuous coral reef included in