The Science of Fingerprints | Page 5

the center
of the divergence of the type lines.
It may be:
- A bifurcation
- An abrupt ending ridge
- A dot
- A short ridge
- A meeting of two ridges
- A point on the first recurving ridge located nearest to the center and in
front of the divergence of the type lines.
The concept of the delta may perhaps be clarified by further exposition.
Webster furnishes the following definition: "(1) Delta is the name of
the fourth letter of the Greek alphabet (equivalent to the English D)
from the Phoenician name for the corresponding letter. The Greeks

called the alluvial deposit at the mouth of the Nile, from its shape, the
Delta of the Nile. (2) A tract of land shaped like the letter "delta,"
especially when the land is alluvial, and enclosed within two or more
mouths of a river, as the Delta of the Ganges, of the Nile, of the
Mississippi" (fig. 19).
When the use of the word "delta" in physical geography is fully
grasped, its fitness as applied in fingerprint work will become evident.
Rivers wear away their banks and carry them along in their waters in
the form of a fine sediment. As the rivers unite with seas or lakes, the
onward sweep of the water is lessened, and the sediment, becoming
comparatively still, sinks to the bottom where there is formed a shoal
which gradually grows, as more and more is precipitated, until at length
a portion of the shoal becomes higher than the ordinary level of the
stream. There is a similarity between the use of the word "delta" in
physical geography and in fingerprints. The island formed in front of
the diverging sides of the banks where the stream empties at its mouth
corresponds to the delta in fingerprints, which is the first obstruction of
any nature at the point of divergence of the type lines in front of or
nearest the center of the divergence.
[Illustration: 19]
[Illustration: 20]
In figure 20, the dot marked "delta" is considered as the delta because it
is the first ridge or part of a ridge nearest the point of divergence of the
two type lines. If the dot were not present, point B on ridge C, as shown
in the figure, would be considered as the delta. This would be equally
true whether the ridges were connected with one of the type lines, both
type lines, or disconnected altogether. In figure 20, with the dot as the
delta, the first ridge count is ridge C. If the dot were not present, point
B on ridge C would be considered as the delta and the first count would
be ridge D. The lines X--X and Y--Y are the type lines, not X--A and
Y--Z.
In figures 21 to 24, the heavy lines A--A and B--B are type lines with
the delta at point D.

[Illustration: 21]
[Illustration: 22]
[Illustration: 23]
[Illustration: 24]
[Illustration: 25]
[Illustration: 26]
Figure 25 shows ridge A bifurcating from the lower type line inside the
pattern area. Bifurcations are also present within this pattern at points B
and C. The bifurcation at the point marked "delta" is the only one
which fulfills all conditions necessary for its location. It should be
understood that the diverging type lines must be present in all delta
formations and that wherever one of the formations mentioned in the
definition of a delta may be, it must be located midway between two
diverging type lines at or just in front of where they diverge in order to
satisfy the definition and qualify as a delta.
When there is a choice between two or more possible deltas, the
following rules govern:
- The delta may not be located at a bifurcation which does not open
toward the core.
In figure 26, the bifurcation at E is closer to the core than the
bifurcation at D. However, E is not immediately in front of the
divergence of the type lines and it does not open toward the core. A--A
and B--B are the only possible type lines in this sketch and it follows,
therefore, that the bifurcation at D must be called the delta. The first
ridge count would be ridge C.
- When there is a choice between a bifurcation and another type of
delta, the bifurcation is selected.
A problem of this type is shown in figure 27. The dot, A, and the

bifurcation are equally close to the divergence of the type lines, but the
bifurcation is selected as the delta. The ridges marked "T" are the type
lines.
[Illustration: 27]
[Illustration: 28]
- When there are two or more possible deltas which conform to the
definition, the one nearest the core is chosen.
Prints are sometimes found wherein a single ridge enters the