CXVill PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
parts of the world containing borax in solution. Boracic acid and 
the borates may be certainly more abundant than is commonly sup- 
posed. Asa constituent of schorl the former is much imtermingled 
with the granites of Cornwall and Devon, and is more especially 
common in the schorl rocks, often occupying the outer part of these 
granites. In estimating the relative amount of boracic acid in schorl- 
bearing rocks, we should recollect that the mean of six analyses of 
black tourmalines, by Gmelin, gives 3°49 per cent. of that acid in 
their composition. We have also to reflect, that other substances 
may play the same part relatively to certain mineral compounds which 
boracic acid and borax have done for the substances employed im the 
beautiful experiments of M. Ebelmen. 
It is always cheering to witness the application of mathematics to 
our science, showing its connection with those of the highest order. 
The labours of our colleague Mr. Hopkins in this field have, during 
the past year, been extended to a consideration of the Internal Pres- 
sure to which Rock Masses may be subjected, and its possible influ- 
ence in the production of laminated structure. Referring to the lami- 
nation, so commonly known as cleavage, he points to the finest and 
most regular as leaving “‘no doubt of its being the result of some 
kind of molecular action of the constituent particles on each other, 
analogous to that of crystallization, and not the direct and immediate 
mechanical effect of external forces acting on the mass.” It i8 
scarcely necessary to state that this is the view taken by Professor 
Sedgwick, and that it is one in which we have long participated. When 
we consider the discoveries and researches of Faraday and others re- 
specting the properties of matter, we seem to have forces acting on 
the great scale amply sufficient to produce such minor effects as we 
have then to consider jointing and cleavage to be. Indeed, looking 
at the arrangements of the mimeral masses, their varied composition, 
and the general conditions under which they are placed, it is difficult 
to conceive that the particles composing them should not be sub- 
jected to influences thus affecting their ultimate arrangement. When 
we find pebbles, even as large as the head, cut through by joints, 
and are unable, by the most careful examination, to detect any shift- 
ing on the two sides of the joints, the surfaces of the latter most 
beautifully plane, with no appearance of splitting according to minor 
differences of resistance, such as we might anticipate in a mechanical 
fracture through conglomerates, we seem to have before us the effects 
of some great power, which can cut through pebbles, often of the 
hardest substances, adjusting the component matter on the (to us) 
great scale, without reference to such comparatively minor bodies. 
While in the divisional planes, to which the term cleavage has been 
applied, we find a shifting of the particles in the finer rocks, so that 
organic remains in them are contorted or lengthened in given direc- 
tions, this becomes less as the rocks take a coarser character. As is 
well known, while the cleavage, in alternating beds of sandstone and 
slate, may be clearly seen in the latter, it can be often only discovered 
in the former by fracture of the beds, and then frequently it is coarse, 
while the cleavage in the alternating slates may be fine. These are 
