Mountains That Float 



Why? Because the underlying materials are lighter than the mountains 



IN a remarkable series of researches con- 

 ducted by the U. S. Coast and Geodetic 

 Survey, under the direction, first of 

 Professor John F. Hayford, and later of 

 Mr. William Bowie, Chief of the Division 

 of Geodesy, it has been conclusively proved 

 that mountains and continents, and prob- 

 ably islands, float. 



The earth is solid. How, then, can we 

 say that the mountains float? 



A hundred or even a thousand years are 

 as a day in the geological calendar; and 

 for such periods the movement of portions 

 of the earth, under any forces which may 

 act on them, would probably be so small 

 as to go unnoticed. But when such forces 

 act for a hundred thousand or a million 

 years or longer, the earth's materials 

 behave as if they were plastic; in other 

 words, they give way to the forces affecting 

 them, and assume a state of equilibrium. 

 Those who work in the deep mines of the 

 earth are familiar with the movement or 

 creeping of the rock which will close old 

 shafts or tunnels. 



But what is the evidence that mountains 

 float ? The answer is in the observed tilting 

 of the plumb line and in the measurements 

 of the earth's pull, called gravity. 



The Proof Furnished by Gravity 



Let us confine our attention to gravity. 

 If the earth's material were a perfect 

 liquid, its surface would be perfectly 

 smooth and the shape of this surface would 

 be that of a ball. Since the earth spins very 

 rapidly, centrifugal force is set up which 

 causes the maximum at the equator and a 

 minimum or zero at the poles. This means 

 a shortening of the axis of rotation by a 

 distance of about twenty-six miles. That 

 is, the distance from the north pole to the 

 south pole would be that much shorter 

 than the distance through the earth's 

 center between two points opposite each 

 other on the equator. 



Exactly the same shape would result if 

 the earth's material, though solid, were 

 arranged in layers according to the density, 

 the densest material at the earth's center 

 and the lightest at the surface. The earth 

 would assume that shape because of the 

 yielding under the attractive force of each 

 particle of the earth's material on every 



other particle, and because of the centrif- 

 ugal force due to the earth's rotation 

 which tends to throw its materials out into 

 space. 



The resultant of these forces, or gravity, 

 would on this ideal earth vary gradually 

 in intensity from the equator to the poles. 



How We Get the Idea of Floating 



The earth's materials are not arranged 

 in layers exactly with respect to their 

 densities. As a matter of fact gravity 

 determinations show that the materials 

 under the vast plains along the coasts are 

 arranged very nearly in the normal way, 

 but that the materials under the mountains 

 are found to be lighter than normal. The 

 deficiency of material under a mountain 

 down to a depth of about sixty miles below 

 the sea level is almost exactly equal to the 

 mountain material which is above sea level. 



Similarly, under plateaus like those of 

 our Western States, there is a deficiency of 

 materials very nearly or exactly equal to 

 the mass of material between the surface 

 and the imaginary sea level surface beneath. 

 The normal density is that under the 

 coastal plains. 



As a result of this counterbalancing of 

 the material above sea level at any part 

 of a continent by material lighter than nor- 

 mal under it, the pressure or weight of 

 material on an imaginary surface about 

 sixty miles below sea level is the same at 

 all points of that surface. 



This brings out the idea of floating. If 

 we should see an iceberg floating in the 

 ocean, we would conclude that the ice 

 showing above the water is held up or 

 floated as a consequence of a greater mass 

 of ice under it. As all know, ice is lighter 

 than water. A block of wood thrown in the 

 water has some of its material held above 

 the surface by the portion under the 

 water. The weight of the material of the 

 whole block exactly equals that of the 

 water displaced by the block. Similarly the 

 weight of a mountain mass and the column 

 of material directly under it to a depth 

 of say sixty miles, below the imaginary sea 

 level surface, equals that of the weight of a 

 similar column of material of equal cross 

 section, under the coastal plain, which 

 has little or no material above sea level. 



