The Elements of Geology

The geological agencies which we have so far studied--weathering, streams, underground waters, glaciers, winds, and the ocean--all work upon the earth from without, and all are...

THE RUN-OFF. We have traced the history of that portion of the rainfall which soaks into the ground; let us now return to that part which washes along the surface and is known a...

The last period of geological history, the Quaternary, may be said to have begun when all, or nearly all, living species of mollusks and most of the existing mammals had appeared.

In our excursion to the valley with sandstone ledges we witnessed a process which is going forward in all lands. Everywhere the rocks are crumbling away; their fragments are cre...

THE DRIFT. The surface of northeastern North America, as far south as the Ohio and Missouri rivers, is generally covered by the drift,--a formation which is quite unlike any whi...

With the close of the Permian the world of animal and vegetable life had so changed that the line is drawn here which marks the end of the old order and the beginning of the new...

THE CENOZOIC ERA. The last stages of the Cretaceous are marked by a decadence of the reptiles. By the end of that period the reptilian forms characteristic of the time had becom...

The alongshore deposits which we have now studied are the exposed edge of a vast subaqueous sheet of waste which borders the continents and extends often for as much as two or t...

Connected with movements of the earth's crust which take place so slowly that they can be inferred only from their effects is one of the most rapid and impressive of all geologi...

FLOOD PLAINS are the surfaces of the alluvial deposits which streams build along their courses at times of flood. A swift current then sweeps along the channel, while a shallow...

We have already seen that the ocean is the goal at which the waste of the land arrives. The mantle of rock waste, creeping down slopes, is washed to the sea by streams, together...

The Carboniferous system is so named from the large amount of coal which it contains. Other systems, from the Devonian on, are coal bearing also, but none so richly and to so wi...

WHAT A FORMATION RECORDS. We have already learned that each individual body of stratified rock, or formation, constitutes a record of the time when it was laid. The structure an...

LAND WATERS. We have seen how large is the part that water plays at and near the surface of the land in the processes of weathering and in the slow movement of waste down all sl...

It is because long-continued erosion lays bare the innermost anatomy of an extinct volcano, and even sweeps away the entire pile with much of the underlying strata, thus leaving...

THE EARTH'S BEGINNINGS. The geological record does not tell us of the beginnings of the earth. The history of the planet, as we have every reason to believe, stretches far back...

In North America the Ordovician rocks lie conformably on the Cambrian. The two periods, therefore, were not parted by any deformation, either of mountain making or of continenta...

THE PALEOZOIC ERA. The second volume of the geological record, called the Paleozoic (Greek, PALAIOS, ancient; ZOE, life), has come down to us far less mutilated and defaced than...

We are now to study the geological work of the currents of the atmosphere, and to learn how they erode, and transport and deposit waste as they sweep over the land. Illustration...

Under the action of internal agencies rocks of all kinds may be rendered harder, more firmly cemented, and more crystalline. These processes are known as METAMORPHISM, and the r...

In America the Silurian is not separated from the Devonian by any mountain-making deformation or continental uplift. The one period passed quietly into the other. Their conforma...

Any sudden movement of the rocks of the crust, as when they tear apart when a fissure is formed or extended, or slip from time to time along a growing fault, produces a jar call...

XIV. THE GEOLOGICAL RECORD XV. THE PRE-CAMBRIAN SYSTEMS XVI. THE CAMBRIAN XVII. THE ORDOVICIAN AND SILURIAN XVIII. THE DEVONIAN XIX. THE CARBONIFEROUS XX. THE MESOZOIC XXI. THE...

I. THE WORK OF THE WEATHER II. THE WORK OF GROUND WATER III. RIVERS AND VALLEYS IV. RIVER DEPOSITS V. THE WORK OF GLACIERS VI. THE WORK OF THE WIND VII. THE SEA AND ITS SHORES V...