Walyunga slate 
319 
Figure 3 The marking sequence on side A, as determined by internal analysis. 
top and l.h. edges and most of the bottom. The r.h. 
fractures can thus be considered to be considerably 
younger than the others which may well date from 
the time the object first came to be on the ground. 
The surface of side A, especially the flat panel 
itself, bears innumerable taphonomic markings, 
including pitted impressions of quartz grains, 
'comet-like' marks (pits with tail-like abrasive 
marks), and deeply gouged angular grooves with 
'sculpted' cross-section. The marks are fully 
consistent with those made experimentally by 
angular quartz grains such as those described 
above from the local sediment. It appears that the 
object's flat surface rested against another hard flat 
surface, with quartz grains caught between and 
pressure applied as the object was moved a few 
millimetres. This would be consistent with the 
taphonomic action of trampling by humans or 
other animals, or it could have been caused when 
the object had been stacked with other slates. A 
prominent group of subparallel lines in the lower 
l.h. corner are not so readily explainable. They 
appear not to be intentional and postdate the 
engraved grid marks, as do practically all the 
major taphonomic markings. 
The incised rectangular grid pattern has been 
drawn free hand, although its lines are almost 
rectilinear. The lines reach the edges in several 
places, and appear to predate all the fractures 
shaping the slate. They avoid the l.h. bevelled edge 
which they can be assumed to postdate. The three 
vertical lines are from 115 pm to 130 pm wide. The 
principal upper horizontal line is about 160 pm to 
180 pm, ignoring effects of weathering, kinetic 
damage and diffuse groove edges. The lower 
horizontal line has a width of 140 pm to 165 pm. 
The shorter horizontal lines in the r.h. upper area 
are thinner and less deep (100-125 pm and 110-120 
pm respectively). 
Of particular importance are the r.h. end of the 
lower principal horizontal line, and a distinctive 
change in depth in the upper line, roughly parallel 
to it but a little to the right. In my replication 
experiments on similar stone I was entirely unable 
to produce a similar groove morphology by any 
means other than the reversal (backing up on a line 
already drawn) of a steel point. In establishing the 
effects of various commonly used metal 
instruments that might reasonably have been 
available last century, I found that I could readily 
produce identical features with the point of a steel 
knife. I consider that it is impossible to replicate 
the precise morphology with any stone tool. Using 
a steel tool to engrave a line, the point of 
commencement always results in a sloping, 
concave commencement of the groove, and the 
groove floor bears a distinctive, 'compressed' 
appearance for at least the first 0.8 mm. 
In past years I have conducted replication work 
with stone tools on various similar rock samples of 
low metamorphism (ranging from slate over 
phyllite to low-metamorphism schist). Narrow 
points even of broad chert flakes pressure-spalled, 
even when only slight pressure was applied, and 
would be quite incapable of producing more than a 
slight scratch on this surface without suffering 
damage. Quartz performs only marginally better. 
The production of a groove of 40 pm or 50 pm 
depth demands a certain minimum width of the 
point to prevent it from splintering. My 
experiments suggest that this minimum width of 
the groove is 350 pm. Such stone tool incision 
