DYNAMICAL GEOLOGY. 321 



hensive laws and principles. One of the most distinguished of 

 living geologists, Professor Marcel Bertrand, writes in the pre- 

 face to the French translation of Suess's work, by M. de Margerie: 

 ''The creation of a science, like that of a world, demands more 

 than a single day; but when our successors write the history 

 of our science, I am convinced that they will say that the work 

 of Suess marks the end of the first day, when there was light;' 



Suess has secured almost general recognition for the Con- 

 traction Theory. Yet there are individual attempts to explain 

 mountain-making in some other way. Amongst these the most 

 worthy of note is Mellard Reade's attempt to work out the 

 Huttonian expansion theory in detail and to make it agree 

 with the ascertained facts of modern geology. Mellard Reade 

 made a number of experiments on the expansion of metals and 

 rocks under different modes of heating, and applied his results 

 theoretically to explain the movements within the earth's crust. 



Like James Hall and Dana, Mellard Reade starts with the 

 assumption that mountain-making takes place only in districts 

 of thick sedimentary deposits, and that there is an increase of 

 temperature in those parts of the earth's crust on account of 

 the additional thickness, and therefore proportional with it. 

 Whereas Babbage, Lyell, Dana, and others suppose that 

 the force of expansion called forth by the increase of 

 temperature acts only in linear directions, vertically upward, 

 Mellard Reade shows that this force must tend to expand 

 rocks cubically, i.e., upward, downward, and laterally. The 

 lateral expansion of the rocks in the heated area is resisted 

 by the relatively less heated rocks of adjacent areas, the com- 

 pression of the expanding rocks causing them to fold and buckle. 

 The upper layers being less influenced by the earth's heat than 

 the lower are in a condition of greater tension, while the lower 

 are more strongly compressed. Both are separated by a neutral 

 zone, in which the rocks experience neither tension nor com- 

 pression ; this zone is called the "level of no strain." 



The rocky floor upon which the thick mantle of deposit has 

 gathered necessarily participates in the subsequent rise of crust- 

 temperature, the expansion, and the compression. Therefore 

 the sedimentary strata of high antiquity composing the floor 

 are subjected anew to heat and pressure, are folded and 

 crushed in the most varied manner, and in their plastic state, 

 since they are stemmed back by the lateral resistance of cooler 

 areas and harder masses of rock, they are readily pressed 



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