44 R. T. CHAMBERLIN AND W. Z. MILLER 
undergoing thrusting with respect to that in the lower portion; 
(2) by any factors which will lessen the resistance in the surficial 
portion without proportionately changing that below; and (3) by 
any factors which will increase the resistance of the deeper portion 
of the zone subject to thrusting while the upper portion remains 
‘freer to yield; (6) in heterogeneous material by bedding, or similar 
structures, which present differences in competency of the right 
sort and thus call into operation some of the foregoing factors. 
3. Preliminary piling up of material in the first stages of 
deformation, thus increasing the load and the vertically acting 
gravitative force. The combination of the horizontal thrusting 
force and the vertical gravitative force gives a resultant which is 
inclined downward from the horizontal. Even should faulting 
take place in a plane 45° from this resultant, it would still be 
inclined less than 45° from the horizontal. 
4. Possible minor factors, as heterogeneity of material, length 
of deformed mass with respect to its other dimensions (after analogy 
of long column), shape of deformed mass, etc. 
To these factors, operating in various combinations according 
to the individual peculiarities of each particular case, are attributed 
the low-angle fault planes of the great overthrusts. 
