510 
Van Else—Earth Movements. 
mineral may be of the kind which is capable of changing into an 
entirely different mineral having the same chemical composition. 
In this case the motions are merely molecular, and yet the 
mineral is fundamentally changed. It acts differently in refer, 
ence to light, in reference to heat; it cleaves differently, and 
has various other different properties. For instance, in its 
original condition the filtered light from a white complex ray 
may emerge reddish or brownish, whereas after the transforma¬ 
tion the light which passes through may be green or blue. The 
mineral may have its chemical composition changed. Certain 
elements may be taken from it by percolating waters, or certain 
elements may be added to it or both may occur, any of these 
changes producing a different mineral. The mineral without ad¬ 
dition or subtraction of material may alter chemically into one 
or more different minerals. Finally, the entire mineral particle 
may be taken into solution, and its place be taken by other 
mineral particles. 
As a result of profound erosion in a region, the rocks are 
gradually transferred from deep within the earth to the zone of 
rapid water percolation. The conditions are now favorable for 
change. Where, as a result of continued erosion the materials 
are brought above the level of underground waters, the conditions 
are still more favorable for rapid alteration of the mineral 
particles, for here they are attacked by the powerful chemical 
agents; they are in the zone of active disintegration, decom¬ 
position, and solution. 
At last a mineral particle reaches the surface of the earth. 
It is then directly attacked by the forces of erosion. By them 
it may be altered, or be torn from its matrix, with little or 
no alteration. It may then be caught up by running water, 
and transported to the sea. If decomposed its elements will 
certainly be widely distributed, and if not, it may be mechan¬ 
ically broken into many parts, so that its distribution is scarcely 
less wide, but ultimately much of its material will be deposited 
along the continental border, and be buried under thick de¬ 
posits. It is now in a position where future land areas may 
be formed, and thus its parts may again go through another 
cycle of change. 
