ON SOME OF THE GREATER PROBLEMS OF 
PHYSICAL GEOLOGY. 
BY 
Clarence Edward Dutton. 
[Read before the Society, April 27, 1889.] 
The greatest problems of physical geology I esteem to be: 
1st, What is the potential cause of volcanic action? 2d, 
What is the cause of the elevation and subsidence of re¬ 
stricted areas of the earth’s surface ? 3d, What is the cause 
of the foldings, distortions, and fractures of the strata ? 
The volcanic problem is at present unsolved. Every 
theory or hypothesis thus far offered to explain it goes to 
pieces at the touch of criticism. For elevations and subsid¬ 
ences we are also without any satisfactory explanation. 
But the third problem, the cause of distortions and fractures 
in the strata, looks much more hopeful, and it is my inten¬ 
tion to propose this evening a solution of it, not a new one, 
let me say, but an old one remodeled. Before proceeding 
to discuss it, it is proper to advert to a hypothesis which has 
long been in favor, and which is looked upon by some au¬ 
thorities as affording an explanation. This is sometimes 
called the contractional hypothesis. 
The earth is regarded as being hot within and undergoing 
secular cooling by conduction of heat through its external 
shell and its radiation into space. This loss of interior heat 
is presumed to be accompanied by a corresponding loss of 
interior volume, thus depriving the cold exterior shell of a 
part of its support. In a body so large as the earth the tan¬ 
gential strain set up by this loss of interior support is demon¬ 
strably so great that the outer shell or crust, as it is usually 
called, must be crushed or buckled by it and collapse upon 
6—Bull. Phil. Soc., Wash., Vol. 11. (51) 
