

EFFECTS REFERRED TO THEIR CAUSES. 841 



3. 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. 721. 



4. By gravity. — Acting on a mass supported only at the sides, p. 695. 



V. Veins. 



Pages 108 to 114, 770 to 782. 



VI. Elevations. Mountains. 



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

 on cooling, producing geanticlinals and geosyncliuals, p. 817. 



2. The same, producing a synclinorium or an anticlinorium, p. 821. 



3. The same, resulting in fractures and monoclinal uplifts, p. 818. 



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

 liquid rock or otherwise. 



5. The lateral pressure produced by the gravity of an adjoining uplifted region or 

 mass. 



2. By Upward Pressure. — 1 and 2 as under IV. 



3. Upward pressure from accessions of heat to underlying rocks, p. 811. 



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

 horizontal rocks, pp. 647, 652, 822. 



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

 consequence of a sinking of the ocean's bottom, p. 784. 



2. In consequence of the abstraction of water in the making of rocks, p. 668. 



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

 Glacial period, p. 784. 



VII. Subsidences. 



1 and 2. As under VI. 



3. By contraction beneath from cooling, pp. 721, 821. 



4. By undermining, through subterranean streams, p. 665. 



5. By undermining, through volcanic action, p. 728. 



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

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



would have reached to the top of the fissures whether these terminated in the strata or 

 opened to the surface. It seems probable that the eruptions began in the making, 

 through subterranean movements, and the filling with lava, of a net-work of fissures, 

 which, for the most part, did not extend to the surface. The fissures remained open 

 along their intersections after they had cooled elsewhere, and thus originated the local- 

 ized conduits for the different laccoliths. Trachyte was an especially favorable material 

 for such results, since it is one of the least fusible of lavas, and hence thickens quickly 

 and deeply when the temperature falls. Its rapid cooling would tend to limit the lateral 

 flow of the lavas in the opened chambers, and give it a confining boundary, and so 

 aid in producing the thick form of the laccolith (much like that of a trachyte dome of 

 some subaerial eruptions), and also prevent the loss of energy from indefinite lateral 

 flow. The term laccolith (like monolith in form) is substituted above for laccolite be- 

 cause the termination ite signifies a hind of mineral or rock. 



Such facts point to the conclusion that a like amount of force may have existed in 

 other fissure lava-streams, and have been the occasion of the vast extent of many ig- 

 neous outpourings. They have also an important bearing on the question as to the ori- 

 gin of the ejecting force in non-volcanic igneous eruptions. (See p. 747). As has been 

 suggested by LeConte, a large part of the rock material in many great volcanic moun- 

 tains of the world may have been poured out at the first opening of the vent. 



