JEANCON] EXCAVATIONS IN THE CHAMA VALLEY 23 
of the bowl is 131 mm. in depth. Accompanying it was a pottery 
lid which is 63 mm. in diameter on the bottom, which is flat. The 
top is slightly convex. The interior of the mortar shows very little 
use, but the top, where the lid rested on it, shows much wear. What 
the purpose of this mortar was it is impossible to say. (Pl. 20, B.) 
On acccunt of their beauty and number, the calcite mortars form 
one of the most striking and interesting portions of the whole collec- 
tion. From time to time, in other excavations, mortars of different 
kinds of stone and shapes have been found, but it remained for Po-shu 
to yield the largest and most beautiful group of calcite mortars. 
Ranging from fragmentary parts in the course of construction to the 
finely finished pieces, they enable us to study the whole process of 
manufacture. The material itself is unique. The fact that the 
rhomboidal calcite crystals are only one degree softer than steel pre- 
sented a problem in manufacture, to the man of the stone age, that 
was rather serious. In some cases the crystals were preserved intact 
on the top of the mortar, in other cases they were broken off and 
the surface ground down to a smoothness that was very pleasing 
and must have involved a large amount of labor. Most of the mor- 
tars are of a beautiful satiny white color and where the crystals have 
been left intact the rhomboidal form is very apparent. Plate 19, G, 
is tinted with a ferruginous stain and at first appears to be made 
of rose quartz. This specimen is by far the handsomest in the col- 
lection. A white quartz pestle was found in the top of this mortar. 
The beautiful rose-tinted crystals were left intact on the top and only 
partly ground off from the sides. Inside the bowl can be plainly 
seen the rhomboidal forms of the crystals. Its greatest diameter is 
228 mm. and it is 114 mm. at the highest part. The greatest depth 
of the bowl is 89 mm. The bottom has been smoothed off flat. 
Plate 19, J, contains some mineral as well as calcite, possibly zinc, 
and is extremely heavy. The rhomboidal crystal is missing and 
the material does not appear so hard as the other mortars. 
Plate 19, F, appears at first to be of a different material from the 
others, but responds tc the sulphuric acid test the same as they do, 
although it is somewhat harder. 
Many of the mortars have incisions representing the four cardinal 
points, which may be taken as an indication that they were used 
ceremonially. 
MISCELLANEOUS STONE OBJECTS 
The type of artifact known as arrow shaft straighteners is too well 
known to necessitate any lengthy description. (Pl. 21.) Those found 
at Po-shu present a great variety in materials used in making them. 
Sandstone predominates and there are some made of a very hard stone. 
Some of the pieces have only one groove, some many. 
2209°—Bull. 81—23——3 
