N 
Clay-balls, clc., from Banter Sandstone, Xotts. 
~oon find that the moving clay has left very definite effects on 
the pebbles, as they are both polished and striated. Those 
which are wholly immersed in the clay are more or less polished 
all over, and of those which are studded on the outside, the 
parts embedded in the clay are polished, while where not so 
embedded they retain their normal roughness. This polish I 
c> insider to be due to the moving clay under great pressure. 
W hen we break up one of these masses and examine the con- 
tained pebbles, it is quite interesting to notice the degree of 
polishing which they have received according to the quality 
of the pebble and its position in the clay-ball. For instance, 
a fine grained quartzite pebble will have quite a greasy sheen 
upon it, whereas a coarser grained liver-coloured quartzite 
will only have its polish distinguished by comparison with 
pebbles from the ordinary pebble-bands ; or, in case of those 
sticking on the outside of the clay, by noticing the difference be- 
tween that portion embedded and that not so embedded in 
the clay. 
It has been suggested that the polish is due to a thin 
■ h-posit of silica on the surface of the pebble, but this I hardly 
think to be the case. 
Ordinary quartzite pebbles often have small ‘ pits ’ on the 
surface. If the polish were due to a deposit of silica it is fair 
to -uppose that these ' pits ’ would get a share of the varnish 
and also be polished, but this is not so. All the little ‘ pits ’ 
remain dull and unaltered, the polish occurring only on the 
general surface. 
Let us try and picture to ourselves what has happened. 
Great pressure would be exerted on the clay-balls by superin- 
cumbent strata, and the clay would be pressed hard against 
the surface of the pebbles and into every microscopic ‘ pit ’ on 
such surface ; from some cause or other motion has then 
taken place in the clay, and the two surfaces of clay and stone 
have moved on each other in a kind of shearing plane, and the 
clay fillings in the little pits have been slid over and not moved. 
Again, when an embedded pebble lies flat in a lenticular 
clay-ball, the flat surfaces of the pebble, or those subjected 
to the greatest pressure, are polished more than the outer 
edges where the pressure is less direct. Had the polish been 
due to deposited silica, then the edges should show an equal 
polish with the flat surfaces. True, sometimes the edge of a 
stone is the most polished, but this is wholly because of its 
position, and this only demonstrates that the polishing is due 
to friction. 
When examined under the microscope, or by a good 
pocket lens, many of the pebbles exhibit a well striated surface, 
sometimes across the stone, sometimes lengthwise, but the 
strife never cross each other. 
Naturalist, 
