442 
E. J. Hebert — Reversed Faults in States. 
sawn through diagonally as indicated; apply equal and opposite 
pressures P, P, Q, Q, at riglit angles to each of the sides, at their 
middle points, as indicated by the arrows in Fig. 1. Then if P be 
T 
P 
Fig. 3. 
equal to Q, there is no tendency to a displacement ; whereas if P 
be greater than Q, the square has a tendency to assume the form of 
Fig. 2, and if P be less than Q, of Fig. 3. Now suppose this 
square, instead of being of wood, and lying on a table, forms a part 
of the earth’s crust, and Stands vertically, the grain of the wood 
being replaced by the strata of whicli the crust is made up ; then if 
the vertical pressures upon the sides of this square of rock exceed 
the horizontal, the strata of which it is made up will tend to 
assume the form indicated by Fig. 2, i.e. a direct fault will probably 
take place ; whereas if the horizontal pressures exceed the vertical, 
the strata will tend to take the form of Fig. 3, i.e. a reversed fault 
will probably ensue. 
These tendencies, however, will not of necessity result in faults, 
since any displacement may be prevented by the more or less rigid 
connexion of the square of rock, under consideration, with the 
adjoining strata, of which it forms a part. Friction also, as well as 
a multitude of other modifying causes, will influence the result. 
Now since it is probable, where strata are tolerably free from con- 
tortion, as in the English Coal-measures, that vertical pressures 
liave exceeded horizontal pressures, (arguing as above) we should 
here expect to meet with direct faults ; but since it is certain in 
liighly contorted and cleaved strata, as in the English and Welsh 
slates, that horizontal pressures have at one time far exceeded the 
vertical pressures, we should here similarly expect to meet chiefly 
with reversed faults ; and in each case our surmises would prove 
correct. 
It should, however, be remarked, that the above are consideration s 
of the rnost simple case, and in practice we should meet with many 
variations which would modify the result. First and foremost 
amongst tliese should be mentioned that the hade of the faults will 
seldom happen to be 45° (as in the figures), a lower hade tending to 
neutralize the motive power of the vertical pressures, and a higher, 
that of the horizontal pressures, while if the fissure be vertical, the 
horizontal pressures will have no motive power at all. Still further 
