152 B. Smith—Ball or Pillow-form Rocks. 
Current Action. 
The disturbing effects of current-action can indeed be demonstrated ; 
for semi-rounded lumps of sandstone (1-2inches across, in Llwyn Bryn 
Dinas Wood) occur in the shales lying between the thicker lenticles 
of sandstone, as if thin layers had been deposited and subsequently 
broken up, rolled along, and embedded in the mud. Conversely, the 
thicker sandstones contain little strips, angular pellets, or rounded 
pebbles of mudstone—proving without doubt that the beds were 
frequently torn up when they had barely attained a state of 
consolidation. 
We may compare such destructive current-action with that to 
which I ascribe the contortions in the dolomitic sandstones in the 
Keuper Marl of Nottinghamshire.’ In this connexion also, the 
occurrence of structureless sandstone in which the balls or pillows are 
embedded is suggestive. 
Thus, although I am not an advocate of the efficacy of current- 
action to form the large ball structures met with in these Paleozoic 
sandstones, but prefer to think they are chiefly due to gravitational 
creep in lenticular beds, I am of the opinion that currents have 
played a greater part in aiding such movements than some geologists 
might admit. 
Effects of Cleavage. 
The effects of cleavage may now be considered. During the process 
of shearing and compression that induced cleavage the irregular 
lenticles of sandstone acted as resistant cores or sheets, and only 
yielded to the impressed forces after a struggle. In some cases they 
slid bodily through the shales, which were caused to flow round 
them like so much butter; in other cases they were bent and folded ; 
whilst in others, again, they were faulted or broken into small 
masses—like the quartz veins in the Ilfracombe slates. The latter 
condition is so common that it is inadvisable to rely upon a dip taken 
in any small isolated mass of banded sandstone, for I have frequently 
found the true dip of the enclosing shales to be almost at mght 
angles to that of the broken lenticle. 
When the sandstones occur as large lenticles or clusters, the 
boundaries of the mass, or group, are often faulted, and the combination 
buckled into folds—structures which may be further complicated by 
post-cleavage movements. The shaly portions of the combination are 
frequently cleaved, whilst at other times the sandstones are cleaved 
as well. In the latter case the angle of cleavage in the sandstones is 
invariably higher than it is in the shales: an effect that would seem 
to imply that the thickness of the shale-belts, relative to that of the 
sandstones, has been decreased by cleavage-shear, and that the higher 
beds of sandstone have moved further than those below. 
In the heart of a thick mass of sandstone cleavage has had little or 
no effect upon the relations of the ball structures to their surroundings ; 
but where they occur at the margin of a lenticle (a very likely position) 
and where lumps of sandstone in the first instance have been detached 
1 “The Upper Keuper Sandstones of East Nottinghamshire ’’?: GEOL. MAG., 
1910, pp. 302-11. i 
