SHAPING THE EARTH — BOWIE 345 



Leith advises the student of the earth to be cautious in any accept- 

 ance of a simple and definite exphmation as to the causes of structural 

 changes near the earth's surface. He claims that "The problem 

 includes so many unmeasured and perhaps immeasurable factors that 

 no living scientist can claim even an approximately correct perspec- 

 tive ; all are groping for the light." 



I agree with Doctor Leith that the problem involved in untangling 

 the geological record is a very complicated one, but I do not think 

 it is wise to advise a student to avoid a simple explanation of some 

 phenomena if other explanations are not available, or if the others 

 are so complicated as to leave one mystified and confused. I believe 

 that the only way to attack any scientific problem is to follow a lead, 

 no matter how simple, until evidence may show that one is not travel- 

 ing in the right direction. 



CONCLUSION 



Isostasy is now widely recognized as a scientific principle. Its 

 advocates hold that there is a maintenance of the isostatic equilib- 

 rium as materials are moved from one place to another over the 

 earth's surface. These are the physical facts which are related to 

 the processes involved in changes in the earth's surface. They have 

 been proven by actual physical measurements. It has been stated 

 that there are great horizontal movements in mountain areas, but 

 that isostasy and its maintenance call for only vertical movements. 

 My answer to this is that I recognize the horizontal movements in 

 mountain areas, but believe that these horizontal movements are 

 incidental to the vertical movements which are involved in main- 

 taining the isostatic balance and which also result from the changes 

 in the temperature of crustal matter brought about by the mainte- 

 nance of equilibrium. There is an abundance of space in a mountain 

 area for horizontal movements to occur, and it seems to me that it is 

 easier to explain these movements as resulting from upward or down- 

 ward moving material than as resulting from a shrinking interior 

 of the earth and a collapsing crust. 



Isostasy is a geological problem. It was outlined by the great 

 geologist, C. E. Button. It has been used by the geodesists merely 

 as an effective means by which to harmonize theoretical and observed 

 values of geodetic data. The geodesists hope that isostasy may 

 prove of great value to geologists in their efforts to write the geolog- 

 ical history of the earth. 



