The Elements of Geology; Adapted to the Use of Schools and Colleges Part 19

What is the general conclusion from these facts?

Why is this conclusion an important one?

What objection to it has been raised?

How is this objection answered?

What additional explanation is given?

CHAPTER III.

SECTION I.

What is the deepest geological change of which we have any knowledge?

What are the reasons for supposing that the lowest stratified rocks are undergoing fusion?

Why are the lowest stratified rocks regarded as of mechanical origin?

What changes have they undergone?

SECTION II.

In what state were the stratified rocks deposited? What change have they undergone in this respect? How is the fissile structure produced? How is the cleavage structure produced?

[Ill.u.s.tration: Fig. 48.]

What is the third cla.s.s of changes?

What do fractures at the surface become by the erosion of water? How are caverns formed?

Describe a vein of segregation. A dike. A mineral vein. What is a fault?

Were the inclined strata thus deposited?

How is it proved that they have taken the inclined position since they were deposited?

What is the direction of the dip?

What lines form the angle of inclination?

What is the outcrop of inclined strata? The strike?

[Ill.u.s.tration: Fig. 49.]

[Ill.u.s.tration: Fig. 50.]

[Ill.u.s.tration: Fig. 51.]

[Ill.u.s.tration: Fig. 52.]

[Ill.u.s.tration: Fig. 53.]

Describe an anticlinal axis. A synclinal axis. A valley of elevation. A valley of subsidence.

[Ill.u.s.tration: Fig. 54.]

[Ill.u.s.tration: Fig. 55.]

[Ill.u.s.tration: Fig. 56.]

When are strata unconformable?

What other disturbances have taken place in the strata?

When did these various disturbances take place?

How is it known that there has been no period of universal disturbance?

SECTION III.

How is it known that the mountains have been covered by the ocean?

[Ill.u.s.tration: Fig. 57.]

[Ill.u.s.tration: Fig. 58.]

Were the granitic ridges thus covered?

Has the level of the sea been, to any considerable extent, fluctuating?

How, then, have the rocks, of which the mountain ma.s.ses consist, been covered by sea?

Give the evidence that different mountains were elevated at different times.

Has the process of upheaval been sudden or gradual?

How are the mountain valleys, which have the direction of the mountain ranges, been produced?

[Ill.u.s.tration: Fig. 59.]

How is the existence of submarine mountains shown?