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POPULAR SCIENCE REVIEW. 
Lingula grits, followed by blue slaty rocks of the Bala or Caradoc 
series, capped by (a), which is a boss of porphyrite without visible 
quartz ; the lines b and c denote respectively the planes of stra- 
tification and cleavage. 
Fig. 2. Diagram showing the relations of the cleavage lines when cutting 
across a broad but thin quartz bed ; the upper plane is an at- 
tempt to represent the distortion of ripple marks occurring on a 
plane of stratification affected subsequently by cleavage, which 
renders them jagged and irregular by the compression they have 
undergone. A fine example of this may be seen on the roadside 
between Pont Aber Glaslyn and the Croesor Valley, North "Wales. 
Fig. 3. Shows the edge of a slate from Llanberris, North Wales, which, 
instead of being straight, has numerous bends, owing to the 
cleavage lines being deflected when passing through thin slate 
beds of unequal hardness. 
Fig. 4. Ideal section of a slab of slate from the Penrhyn slate quarry at 
Bangor, containing a hard pebble of diabase inclosed in the 
Cambrian slate : although interrupting the cleavage lines, its 
major axis lies parallel to them. 
Fig. 5. Yellowish concretions in the purple Cambrian slates of Llanberris, 
(a) in plan, (6) in section, showing how they lie flattened out 
in the line of cleavage and cut through by the cleavage planes. 
Fig. 6. A farthing in its normal condition (a) ; ditto, after passing it 
longitudinally between the rolls (6) ; and the same, transversely 
(c), showing how the image becomes distorted lengthwise or 
crosswise, according to the direction in which it is rolled. 
Fig. 7. Section of a mass made up of pipe-clay and smithy scales (a), and 
a section of the same edgeways, after being compressed to one- 
half its volume ( b ) (Sorby). 
Fig. 8. Microscopic section of ordinary slate rock, (a) uncleaved, (6) 
cleaved. 
Fig. 9. Asaphus Homfrayi (Salter), a trilobite from the Tremadoc beds, 
{a) but slightly flattened out, (6) distorted by cleavage. 
Fig. 10. Sections of devonian encrinite limestone from Devonshire, (a) 
cleaved ; (6) uncleaved (Sorby). 
Fig. 11. Vertical section seen in the cliffs near Ilfracombe (Sorby), show- 
ing the crumpling up of hard arenaceous beds when they occur 
in well-cleaved slate. 
Fig. 12. Figures (a, b , c ) of normal Euomphalus pentangvlatm , and the 
same distorted in two directions, from Little Island, co. Cork 
(Haughton). 
Fig. 13. Diagram of a stone quarry, which shows the occurrence in one 
mass of rock of stratification ( b b) f cleavage (c c), and parallel 
joints (jj) (Murchison). 
Fig. 14. Lozenge or rhomb-shaped fragment of Cambrian purple slate from 
Llanberris, North Wales, showing the cleavage planes ( b c), 
bounded by two smooth joints ( a b ), and the colour bands or 
stratification (d d), all in a hand specimen of about 4"x2"xl" 
in dimension 
