The Elements of Geology; Adapted to the Use of Schools and Colleges Part 15

How is this demonstrated?

What is the relative position of the older and newer granites?

What other plutonic rocks occur in considerable quant.i.ties?

SECTION III.

Of what do volcanic rocks consist?

 

In what states are they ejected?

What are the princ.i.p.al varieties of lava, and how are they distinguished?

Why is the basaltic lava the last to be ejected?

How is the age of the volcanic rocks determined?

What are the three divisions of the volcanic rocks, as dependent upon age?

What is the proportion of the volcanic to other rocks?

How many active volcanoes exist?

Describe the eruptions of Kilauea.

Describe the eruption in Iceland in 1783.

What are the dimensions of Mount aetna, and how has it been produced?

How are the tertiary lavas known to be such?

Where have they been most studied?

What is the evidence that these rocks in France are volcanic?

Have these lavas been produced within the historic period?

[Ill.u.s.tration: Fig. 5.]

Were they produced at an early period in the earth's history?

Give the evidence that their activity was long-continued.

[Ill.u.s.tration: Fig. 6.]

What is the form of the earlier volcanic rocks?

What circ.u.mstances distinguish the trappean from other volcanic rocks?

What are some of the prominent localities of the trappean rocks?

How do they occur in the islands west of Scotland?

How in the valley of the Connecticut river?

SECTION IV.

What is the lowest metamorphic rock?

Describe it.

How does mica slate differ from gneiss?

Is it well distinguished from argillaceous slate?

What is the third rock in the metamorphic series?

Why is it difficult to determine the upper limit of this series?

Why do the princ.i.p.al rocks of this series occur in the order here given?

What other rocks may take the place of these princ.i.p.al rocks?

Where do the metamorphic rocks occur?

What is their thickness and amount?

SECTION V.

How many systems of fossiliferous rocks are there, and what are they?

What other system is provisionally introduced?

What is its position?

[Ill.u.s.tration: Fig. 7.]

Describe it.

What materials of value are obtained from this system?

[Ill.u.s.tration: Fig. 8.]

What fossils does it contain?