732 C. R. VAN HISE 



hypothesis ; and it further seems to me that observed geo- 

 logical phenomena also disprove it. 



I have elsewhere divided the outer crust of the earth into 

 zones, in descending order as follows: a zone of. fracture, a 

 zone of combined fracture and flowage, and a zone of flow- 

 age. 1 



Now, we will suppose that the crushing strength of the 

 strongest rock is such that at a depth of twenty thousand meters 

 below the surface the weight of the superincumbent rock (less 

 the floating effect of underground water) is as great as the 

 crushing strength of the rock. We will suppose that such a 

 rock as the Berlin granite of Wisconsin, the strongest rock yet 

 tested, having a crushing strength of 47,674 pounds per square 

 inch, 1 extends from the surface to an indefinite depth. We will 

 further suppose that in some way openings of some kind, say 

 large cracks, are produced at the depth where the rock is under 

 weight as great as its crushing strength. What would happen? 

 You engineers know very well the rock would be crushed and 

 the openings would close. Therefore at a depth of more than 

 20,000 meters below the surface of the earth, where the weight 

 of the superincumbent rock is greater than the strongest rocks, 

 if it be supposed that cracks of a considerable size could be 

 formed, the pressure would crush "the rocks and close the cracks. 

 But the crushing strength of the great majority of the strong 

 rocks does not exceed one half that of the Berlin granite. More- 

 over rocks at considerable depth are at higher temperatures than 

 normal, and this probably weakens them. Consequently upon 

 physical grounds we are prohibited from supposing that there 

 are cracks and crevices of considerable size at more than a very 

 moderate distance below the surface of the earth. But this con- 

 clusion does not rest upon physical principles alone. I have 

 shown that there is another way besides crushing by which 



1 Principles of North American pre-Cambrian Geology, by C. R. Van Hise : Six- 

 teenth Ann. Rept. U. S. Geol. Surv., 1894-5, Pt. I, p. 589. 



2 Building and Ornamental Stones of Wisconsin, by E. R. Buckley : Bull. Wis. 

 Geol. and Nat. Hist. Surv., No. 4, 1898, p. 390. 



