15 
doctrines remain mere unTerified conjectures; the atomic 
history of the universe is yet to be constructed. We do not 
accurately know what takes place when a piece of india- 
rubber is bent or a piece of moist clay is squeezed into a new 
shape. Still we are in the way of progress when we collect 
and sift facts, arrange them into classes under general pro- 
positions, and test those propositions by applying them to 
fresh cases. Hereafter it will be possible to apply one 
principle to explain at once the fluidity of water and the 
contortion of rocks. Even now we can group together the 
past and the present, the great and the small. We can show 
that the forces which arched the Silurian rocks of "Wales 
are still operative, and that the same forces can be displayed 
and recognised in the laboratory of the student. 
EXPLANATION OF PLATE. 
Fig. 1. Contortion apparatus. 
a. Cylinder containing shot. 
6. Rod connecting a with the vertical plate c. 
d, d. Frame in which the plate c slides. 
e. Knife-edge, hinged on c. 
/. Iron block, gliding in groove h, to which the lamina k is fixed by the 
screw g. 
i. Apparatus for setting the index I at zero in any position of the vertical 
plate. 
I Index moving over a graduated arc. 
m. Index moving backwards and forwards to show the deviation of e from 
the perpendicular. 
Scale nearly y of the actual machine. 
All the parts are iron or steel, except the cylinder a, the rod 6, the indices 
and the scale, which are brass. 
Figs. 2, 3. Examples of distorted pebbles in conglomerate at Newport, 
Rhode Island, reduced fr«m Memoirs of the Boston Society of Natural 
History, vol. i. pi. 17, 18. 
The Plate was prepared to illustrate an article on the Contortion of 
Rocks, which appeared in the Popular Science Review, for January, 1872. 
"We are enabled to reproduce it here by the courtesy of the Publisher of the 
Review, 
