r that the _mere converging of two ridges
does not form a recurve, without which there can be no loop_. On the
other hand, there are many patterns which at first sight resemble
tented arches but which on close inspection are found to be loops, as
where one looping ridge will be found in an almost vertical position
within the pattern area, entirely free from and passing in front of
the delta.

Figure 134 is a tented arch. The ridge marked "A--A" in the sketch
enters on one side of the impression and flows to the other with an
acute rise in the center. Ridge C strikes into A at point B and should
not be considered as a bifurcating ridge. The ridges marked "D--D"
would form a tented arch if the rest of the pattern were absent.

[Illustration: 134]

[Illustration: 135]

Figure 135 is a sketch of a pattern reflecting a ridge, A--B, entering
on one side of the impression, recurving, and making its exit on the
other side of the impression. The reader should study this sketch
carefully. It should be borne in mind that there must be a ridge
entering on one side of the impression and recurving in order to make
its exit on the same side from which it entered, or having a tendency
to make its exit on that side, before a pattern can be considered for
possible classification as a loop. This pattern is a tented arch of
the upthrust type. The upthrust is C. There is also an angle at E. D
cannot be termed as a delta, as the ridge to the left of D cannot be
considered a type line because it does not diverge from the ridge to
the right of D but turns and goes in the same direction.

In connection with the types of tented arches, the reader is referred
to the third type. This form of tented arch, the one which approaches
the loop, may have _any combination of two of the three basic loop
characteristics, lacking the third_. These three loop characteristics
are, to repeat:

- _A sufficient recurve._

- _A delta._

- _A ridge count across a looping ridge._

It must be remembered that a recurve must be free of any appendage
abutting upon it at a right angle between the shoulders, and a true
ridge count is obtained only by crossing a looping ridge freely, with
a white space intervening between the delta and the ridge to be
counted.

[Illustration: 136]

[Illustration: 137]

Figures 136 and 137 are tented arches having loop formations within
the pattern area but with deltas upon the loops, by reason of which it
i