30-1- 
THE GEOLOGIST. 
ject are also well brought out to view, and exposed for solution by 
subsequent observers. Not mucli, however, has been done since the 
date of that memoir. Mr. Ormerod's communication on the Rock- 
basins of Dartmoor, in the Geological Society's Journal, 1858, vol. 
xiv., p. 16, &c., contains a resume of our present knowledge on the 
subject, and to this we shall presently recur. Fig. 5 represents one 
of the Dartmoor tors, the granitic boss known as Blackistone ; and 
fig. 3 is a sketch of Haytor (eastern side), also in Dartmoor. The 
latter is from my note-book ; and, in connection with some appear- 
ances on the faces of the granite-quarries on the lower ground to 
Lign. 5. — Blackistone, Dartmoor. 
the westward, offers an interesting illustration of the method of the 
formation of " tors," " cheesewi'ings," and " logging stones." 
A few hundred yards below Haytor is an old quarry, the smooth 
ftices of which are formed of the joint-planes of the granite. These 
faces show many of the cross-joints ; and on the eastern face the 
north-and-south pei'pendicular joints are plainly seen here and there 
to be the channels by which the rain and frost are working their 
way into the rock, producing innumerable minute cracks close to 
and mostly parallel with the great fissures (fig. 6). This is especially 
the case beneath the siirface-soil, where the joints are enlarged into 
a compound group of cracks, minutely cutting up the stone into 
