442 GEORGE F. BECKER 
is manifest that all possible resistances are included. The inde- 
pendent class are the elastic resistances. The resistances which 
depend on the rate of straining are the viscous resistances. 
Examples of viscous resistance are seen in the rapid subsidence 
of vibration ina tuning fork. If steel were an ideal elastic solid, 
a fork in a vacuum would vibrate forever. If rubber were ideally 
elastic, a band supporting a weight and stretched so as to make 
the weight dance up and down would continue to stretch and 
contract indefinitely, while in reality the action ceases in two or 
three seconds. If a weight is suspended on a wire for a second, 
the wire may be practically unimpaired by the strain, when the 
same weight left for a minute would seriously elongate the wire. 
Flow in such a wire is a process which demands time; and there- 
fore it involves viscosity. Such illustrations show that viscos- 
ity is not a merely recondite property of matter which can be 
relegated to theoretical physicists and neglected by geologists. 
It is absolutely certain that it must play as important a part in 
geological deformation as the elastic forces. During an instant 
of time elastic and viscous resistance are indistinguishable and 
they coéperate with one another to resist deformation. When 
one considers a very long period of time instead of a very short 
one, viscous resistance almost disappears and it vanishes utterly 
when the time is infinite. It is easy to see that this must be 
true; for the intensity of resistances which continue to exist 
after an infinite time is independent of time. Hence, if any mass 
is strained for a short time its resistance is the sum of its elastic 
and viscous resistances. If it is strained for a long time, on the 
other hand, only the elastic resistances will oppose deformation. 
Again, if a body is strained for a brief period in one direction 
and for a long period in another, it will act as if it were strong 
in the former direction and relatively weak in the latter. 
In scission the sheets of the mass parallel to the fixed sup- 
port are constantly impelled to glide over one another by the 
maximum tangential load and if the forces act for a long time 
the flow in this direction is opposed only by the elastic resist- 
ance. In the other set of planes of maximum tangential load in 
