204 
of P. B. Brodie, F.G.S. This course of geodes is persistent, 
equally occurring at Churchdown, and with the same contents : 
broken bits of shells and of crustacea, containing also fish re- 
mains and insects in some places, though none of the latter 
were met with at Alderton. 
LITHOLOGY 
The so-called “Paper Shales,” forming the capping of 
Alderton Hill, are of a dark puce colour, nearly black; their 
origin is clearly from the “‘smatches ” of the coal measures up 
country from the Clee Hills and Forest of Wyre district. They 
are more or less bituminous, as well as carbonaceous, and uni- 
formity and regularity of the thin films would denote a quietly 
deposited sediment, free.from disturbing currents. It has been 
noticed by Sorby that fine grained mud obtained from a depth 
of 2,600 fathoms in the South Pacific, possesses the following 
remarkable property, which throws light upon the formation of 
the concretions known as the Fish bed, or by Brodie as the 
Insect bed. The grains of sand do not separate from the finer 
mud and subside, but gather the finer particles about them into 
a compound granule, and this process rapidly clears the water. 
It has been determined by experiment that the solid matter 
in such muds only amount to eleven per cent., while in shales 
the solid matter is at least seventy-five per cent., so that when 
pressure squeezes the water out of these clays they may be 
reduced to one-sixth of their original thickness; and this change 
would tend to develop in the bedding planes exactly such a 
fissile structure as we witness in the “ Paper shales” of Alder- 
ton Hill. These shales are traversed by joints, which are not 
quite vertical in direction, but which cross each other at a small 
angle. The cause is due to the direction of the mechanical 
stresses, and the result is clearly seen in the section of the 
blocks of clay, the blocks forming neither cubes, nor parallelo- 
grams, but from the oblique direction of the stresses the 
result is, that the forms produced by their intersections give us 
rhombs or rhomboidal figures; and these, together with the 
jointings as apart from cleavages, also common to the Marl- 
stones below, powerfully contribute to shoot off and discharge 
