B. Smith—Ball or Pillow-form Rocks. 153 
and isolated in the shales, the effect of the cleavage has been to jam 
these lenticle-noses or semi-rounded balls into the shales, which were 
thereby slickensided and plastered tightly upon them. Insome cases, 
indeed, a sort of subsidiary cleavage (due to jamming) curves round 
the balls in places where the ordinary cleavage had little effect. 
Fic. 6.—Diagram showing curved cleavage. 
A local curved cleavage, developed in this definite manner, may 
either accentuate the true ball structures, or suggest ball structures 
even when the sandstone lamine do not conform to the curved surface. 
Fig. 6 is an attempt to express these two cases diagrammatically. 
Similar effects are liable to occur also on a large scale about masses 
of sandstone and shale 100—200 feet in thickness, the slickensides being 
represented by faults. In the lee of the mass we may find (taking 
the analogy from a ‘rain-shadow’) a ‘cleavage-shadow ’, or locality 
in which the cleavage is modified or absent owing to the protection 
afforded by the sandstone. 
Some allied phenomena. 
Amongst allied phenomena we might instance the contortions and 
uneven deposition of some of the Wenlock—Ludlow beds of Denbigh- 
shire. These consist chiefly of blue shales with sandy laminz which 
become clustered at frequent intervals to form sandy shales or thin 
beds of sandstone. The clusters are usually only half an inch or so in 
thickness, but some of the sandy beds may attain a maximum of 
6-8 inches. Occasionally the sandy beds are split up by muddy 
Se * 
ee ee 
a ree € Ins 
Se 
Fic. 7.—Folded layers of sandstone and shale, Pant-yr-onn, 
Llanelidan. 
layers. In one case, near Pant-yr-onn, Llanelidan, an 8 in. band of 
laminated sandstone contained 6-7 muddy layers, those near the 
centre of the bed being thrown into gentle undulations, of wave- 
length about 9 inches and amplitude about 3 inches, whilst the upper 
and lower layers pursue a straight course (Fig. 7). Here and there 
the folded bands of mudstone thicken quite suddenly, especially on 
