DYNAMICAL GEOLOGY 
85 
ing movements between rock-masses, accomplished both by frac¬ 
ture and flowage, and caused by stresses inclined to the planes of 
motion. This conception is taken to afford the best initial basis 
for the interpretation and correlation of the observed rock struc¬ 
tures. 
There is no certain evidence of increase or decrease of move¬ 
ment towards the bottom of the zone. Beyond a shallow surface 
zone, there is no certain evidence of increase of rock-flowage 
and decrease of rock-fracture with depth. There is no certain 
evidence that rock-flowage means greater weakness than rock- 
fracture. There is no certain evidence in rock-flowage that pres¬ 
sures are dominantly hydrostatic or dominantly those of compe¬ 
tent solid bodies. 
In the zone below our range of observation movements are 
known to occur, but their nature and distribution are subjects of 
varied hypotheses based upon a few known conditions. Much of 
the sharper diastrophism seems to be confined to a thin surfical 
zone. Deeper movements, of a more massive type, periodic, 
and possibly slower, seem to be implied by the relative movement 
of the great earth segments as represented by the continents and 
ocean basins. Their depths are unknown. 
Most of the current hypotheses agree in assuming a single mo¬ 
bile zone in which rocks move dominantly by flowage. However, 
the basic requirements of reasonable hypothesis may be met equal¬ 
ly well by a conception of movement much like that of the zone 
of observation. This does not require or postulate the conception 
of the existence of any single mobile zone, or zone of slipping, 
or zone of flowage, or of an asthenosphere. It premises movement 
irregularly distributed in many zones, with any inclination, and 
accomplished by both fracture and flowage as far below the sur¬ 
face movement extends — always remembering that some of the 
structures geologically described as fractures, may be expressions 
of mass-movements of the kind defined as flow in experimental 
results. 
With depth, conditions of temperature and pressure and vulcan- 
ism become more intense, but it remains to be shown that conjoint 
action results in a uniform environment and even if it does, that 
this condition is not upset by what might be called a heterogenity 
of the time-factor as represented by different rates of deformation. 
