EFFECTS REFERRED TO THEIR CAUSES. 761 



4. By the action of gravity. — Takes place after an undermining, or a loosen- 

 ing in some way, pp. 645, 654, 655, 713. 



5. By vapors suddenly developed, p. 711. 



IV. Flexures. 



1. By lateral pressure. — 1- The lateral pressure from the earth's contraction 

 on cooling, pp. 736, 738. 



2. The lateral pressure from the expansion of rocks by heat. 



3. The lateral pressure due to the action of gravity, p. 655. 



2. Through the conditions of cooling. — Want of parallelism in the op- 

 posite cooling surfaces of cooled rock, making curved columns in some igneous rocks, 

 p. 701. 



3. By gravity. — Acting on a mass supported only at the edges, p. 681. 



V. Veins. 



Pages 108 to 114, 731 to 734. 



VI. Elevations. Mountains. 



1. By Lateral Pressure. — 1- The lateral pressure from the Earth's contraction 

 on cooling, producing geanticlinals and geosynclinals, pp. 739, 748. 



2. The same, producing a synclinorium or an anticlinorium, pp. 749, 751. 



3. The same, resulting in fractures and monoclinal uplifts. 



4. The lateral pressure, produced by expansion from heat, received from a region of 

 liquid lock or otherwise. 



2. By circumdenudation. — Produced by denudation over a region of nearly 

 horizontal rocks, p. 645. 



3. Apparent elevation due to a sinking of the Water-level. — 1. In 

 consequence of a sinking of the ocean's bottom. 



2. In consequence of the abstraction of water in the making of rocks, p. 657. 



3. In consequence of the abstraction of water to make ice over the land, as in the 

 Glacial period. 



VII. Subsidences. 



1 and 2. As under VI. 



3. By contraction beneath from cooling, p. 701. 



4. By undermining, through subterranean streams, p. 654. 



5. By undermining, through volcanic action, p. 715. 



6. Through contraction from the drying of an undertying bed, as, when a portion of 

 a marsh is drained, the surface of that part sinks below the rest. 



VIII. Valleys. 



1. By Brosion. — 1- Through fresh-water streams, this is the great source of the 

 valleys and gorges in mountainous regions: sometimes, though seldom, the direction 

 is predetermined by fractures, p. 638. 



2. Through marine currents and waves, removing dikes that intersect coast rocks, 

 or portions of yielding rock ; a process which produces small cuts or excavations, but 

 not true valleys, p. 672. 



3. Through the action of glaciers, either b}' the tearing action of the ice, where 

 descending at bottom into cavities in the rocks, or by abrasion carried on by means of 

 the stones in the bottom and sides of the glaciers, p. 539. 



2. By movements of the Earth's crust. — 1. Producing parallel ranges of 

 mountains (synclinoria, or anticlinoria, or both), of which the "Mississippi valley" 

 is an example, pp. 23, 740. 



2. Producing a geosynclinal, p. 740; but the progressing geosynclinal usually be- 

 comes filled with sediment as it forms, and hence does not appear as a valley-depression. 



