100 FRANK D. ADAMS 
certain assumptions and have a probability no greater than the 
assumptions on which they are based. 
The mathematical aspect of this question, however, as well as 
that of certain other questions arising out of the experimental 
results set forth in the present paper are treated at length by Mr. 
L. V. King, of the Department of Physics of McGill University, 
in the accompanying paper. As will be seen, Mr. King is of the 
opinion that the assumptions made by Mr. Hoskins are not per- 
missible. 
But even if the calculation were not based on these doubtful 
mathematical assumptions, a whole series of additional assumptions 
are made which very seriously affect the final result, as Van Hise 
himself points out. These are: (a) that rocks below the surface 
of the earth have the same strength as at the surface; (0) that the 
rocks constituting the earth’s crust are all of the same kind; (c) 
that the temperature within the earth’s crust is the same as that 
at the surface; (d) that the presence of water does not affect the 
character of the deformation; (e) that rocks yield as readily by 
fracture as by flow; (f) that rocks break as readily by fracture, 
when the deformation is slow as when it is rapid; (g) that the 
rocks whose crushing strength is taken as a datum are among the 
strongest in the earth’s crust. 
Van Hise believes that these assumptions are such that could 
we apply corrections for each of the factors concerned, we should 
find that these—with the exception of the first—‘‘would tend to 
lower the figures given, that is to say, to bring the Zone of Flow 
nearer to the earth’s surface.” ‘But I suspect,’ he goes on to 
say, “‘that the various factors giving too great a depth are of far 
greater consequence than the one factor giving too small a depth.’”* 
He suspects the depth given by Hoskins is much too great, “ prob- 
ably twice too great.” 
The circumstance, however, that all these disturbing factors 
exist and that no account is taken of them in the calculation in 
question is frequently altogether forgotten and, consequently, 
positive statements are often made based upon this calculation, 
such as the following from a well-known book which has recently 
appeared. 
1A Treatise on Metamorphism, 180. 
