The Crittenden record. [volume] (Marion, Ky.) 1904-1907, 1906-03-30
,IoN, CRTTTENDEN COUNTY, KY, MARCH 80, 1906.

all types Of tension iissures: Upon
adding 30 deg. TO or subtracting it
from; northeast courses (according as
they may be north-northeast or east
northeasD will give the corresponding
northeast course: for the northwest
courses, add and subtract 60 deg. from
the north-northeast course. or, having
the north northwest course given, add
60. 80 and l2O deg, and obtain the
other three; while II the west north.
west be given, the north northwest
may be obtained by subtracting go deg.
Such bearings may be readily obtained
fundamentally, by constructing an
equilateral triangle. using either the
north northwest, the north north
east, or the west northwest, as a
basal side; the remaining two sides
will then give the bearing Of the other
two, while perpendicular dropped on
the north-northwest side will give the
east-northeast bearing.
Often only two members Of set are
obtained though usually a third is pres
ent. and less often a fourth. In the
Kentucky Illinois district. north
northeast and a nor,h.northwest, with
usually one Of the other two are TO be
found, depending somewhat on what
part Of the field one is in. The pre-
dominance is to be explained upon the
basis Of previous strains producing
lines Of least resistance. In the Ken
tucky-lllinois district such lines are
offered by the crossing Of two mono
clinal folds, forming a fan-like fold,
previous TO the publication Of the forces
resulting in assures and faultings.
Variations from the angles named
are TO be expected. the amount Of
variation being dependent largely on
the extent Of homogeneity Of the rock.
the variation increasing as the extent
Of homogenoity decreases. Amaximum
variation Of ten deg. might obtain.
though in most Instances Il will be less
than five degrees. In any one section
Of a district, one or more sets may
prevail and the presence Of more than
one set may be assumed when two
fractures are found with courses form
ing sn angle largely variant from the
constants given.
The most probable explanation that
presents itself. as to why the direc-
tons assumed by fractures should bear
constant relations Ia each other. so as
to permit their grouping into sets. may
be- statsd thus: Consider a fault zone
as a beam. in which a tension stress
has been induced az an acute angle "a
the axis Of the beam. Where tension
Is set up. shcaring results, at AN acute
angle TO the direction in which the
force Is applied Theoretically. the
angle Of MAXIMUM shear made at righ,
angles with the applied stress. is i5
deg. for both compression and tension.
Practically Il appears 10 be less for
compression and greater for tension.
Ilodgckinson obtained e deg. as an
average for compression Of twenty -on,
cast.irun cylinders: while kircaldy ob.
tanned g. deg with the axis Of tension
Tor tensile stresses In steel Allowing
8 deg. m the latter instance Tor yaria.
tion of chan actcr and homogcncity Of
material acted upon, We have clos,
correspondence with the angle secure,
In the field.
Modifying somewhat the statement
presented by Hoskins. a. To the pro
duction Of fossility by comprcssiy,
stress. We have the following:
Where rocks arr subjected In yolum,
to the forces of compression or tension
in ease of the former the angles formc,
by shears. would be AZ an avcrag,
angle of dcr or & deg. such aver
age still to be determined. while whcr,
tension is the dominant stress. an ap
proach 20 angles of ~ deg may b,
anticipates. In such case. two set
Of planes Of rupture may develop, cut
ting each other at an obliquc angle
/ the greatest pressure hisccting th,
acute angle. for eOmprcssiyc stresses
and cutting each other at IN acut'
angle. the greatest stress biscctirg th
obliqlc angle. for tensile strcHct Th
latter corresponds with the two rrh,
angles formed between the first an
and third and the second and iourtI
members u a set, the angles cuttirl
each other et the acute angle of ,
deg. while such rupture will prolabl
not occur IN regular manner through
out largc volumes. considerable rcgu
latity holds Tor limited volumes. prc
ducing approximate parnlIclism Of faul
planes.
Such strike sets become equally ap
plcablc to the joints. larger fracture
AMI faults. and fracture and fault
soncs. the variation becoming some
what greater as applied to increase
volume. While the course pursucd b
isul, zones. where en- cchelon fracture