16 FLANGES OF AUSTRALITES (TEKTITES) 
being sometimes towards posterior surfaces (PI. I, 6) but more 
frequently along anterior surfaces towards equatorial regions. 
Some main flow lines well within the body are parallel to its 
exterior surfaces (Pl. I, 9), others are radial (PL I, 1). Those 
near anterior surfaces arise in all positions from the front pole 
almost to the flange junction, c, numerous short flow lines 
originating within the body at depths below the surface of from 
0 5 mm. at the junction c, up to 3 mm. near the front pole; these 
unite and form streaks trending more or less parallel to the 
anterior surface. Near and parallel to the posterior surfaces 
main sets of flow lines are rare (PL I, 5), and they seldom trend 
from both anterior and posterior surfaces towards equatorial 
regions (Pl. I, 3). Flow lines close to anterior surfaces are 
generally truncated in flow troughs, but are parallel with those 
in flow ridges (Pl. III, I) ; this indicates some loss of glass in such 
regions, probably caused by ablation during flight. 
Oblique sections across the line of union c (Pl. III, 5) also 
show internal flow lines in the core trending mainly flange-wards, 
but made complex by fold-like structures. Most of the complex 
flow lines within cores were probably formed at an earlier stage. 
Union Between Flange and Core 
Surfaces of attachment between flanges and central cores (c. 
Fig. 1) can be seen on detached flanges free from adhering 
portions of core. Tracks of bubbles and aggregations of bubble- 
pits indicate accumulation of gas in this region ; this must weaken 
the attachment of flange to core and it accounts for the occurrence 
of detached complete flanges. 
The surface of the neck often carries concentric flow lines 
parallel to similar lines on the chin 
In thin section c is invariably a sharp, dark line; and, as 
already remarked, small bubble-pits tend to assemble at or near 
it (PL II, 8 and 11, and Pl. III, 7). Before reaching the anterior 
surface, c usually swings round parallel to the anterior surface 
(Pl. II, 3), ultimately passing into the flange as flow lines; it 
thus marks oft the seat (Fig. 1), a narrow, shelf -like part of the 
core upon which the flange rests. Flow structures in the base of 
the flange are parallel to those of the seat (Pl. II, 4). The seat 
may be small (Pl. II, 8 and 10) or almost wanting (Pl. II, 1 
and 9), probably as a result of ablation during flight. The width 
of glass at b (Fig. 1) ranges from 2 mm. to 6 mm. At the wider 
end of the seat the glass is from 0 5 to 1 mm. thick. 
Australites with small seats associated with plentiful bubbles 
would lose their flanges more readily than would other forms. 
