File:The Quarterly journal of the Geological Society of London (12961600944).jpg

1869.. ORiLEROD— DAETMOOK GRANITE. ,. 277
mile, mark the places to which the granite extended before it curved
down to the N. & S., as before mentioned. At Wattern tor (fig. 2),
Fig. 2. — Wattern Tor, from the South, showing the decay along the
lines of North and South Joints.
the chief mass is crossed by two north and south lines, along which
decay has acted, dividing the upper part into three masses, and
forming one of the most imposing tors on the moor. To the N.E.
of this tor there is a narrow ridge with low cliffs on both sides,
formed by parallel N. & S. lines of joint ; and at one place, in
consequence of decay along the E. & W. joint, the storms have
forced a passage, whence the tor has derived the name of Thirl-
stone. The E. & W. joints here are not perpendicular, but in-
cline towards the south ; at Honey-bag Tor, near Widdicombe, in
the moor, the inclination is towards the north. Near Manaton, on a
hillside, there is a solitary tor, " Bowerman's Nose," rising about 40
feet above a " clatter of rocks ; " its prismatic shape is probably
derived from the intersection of lines of joint. These tors have been
selected from many as a series of examples of the effect of lines of
joint, tracing it from the large massive cluster of rocks to the insu-
lated pillar. Belstone Tors in the hard granite, and Hound Tor in
the softer granite, are probably two of the best points for studying
the hues of joint, and the different varieties of bedding, and decay
along the lines of bedding, that occur in the east of Dartmoor.
It has been before noticed that the granite at the northern part
of Dartmoor is more crystalline and compact than that to the south
of the North Teign ; in the last-named district is the broad belt
extending across Dartmoor mentioned in my paper on Rock Basins,
as containing those hollows (Q. J. G. S. xv. p. 16). In this south-
eastern division, in addition to the other sources of decay, is one
that arises from the spheroidal structure of the granite. Professor
"Warington Smyth, in his Presidential Address for 1868 (page 1.),
mentions that in Palestine blocks of granite decay from the centre