169 • 
In the foregoing table are several terms, which, being provincial 
expressions, may not be generally comprehended. They will, how- 
ever, be understood, probably, sufficiently well for the present in- 
tention : it, however, may not be amiss to observe that clunch, in 
that part of the country to which the above table refers, represents 
the firm blue clay of Wallerius (argilla plastica particulis suhtili- 
orihusj, which is generally used for tiles: and in Cambridgeshire 
the same term is employed to describe a white hard clay, containing 
sand and small stones. 
The line formed by the bearing, or laying of one stratum upon 
another, is called the parting, and according to the facility of 
separation it is named a good parting or a bad parting. Sometimes 
the two strata are so closely conjoined as to render their separation 
very difficult ; this is termed a bad parting. On the other hand, a 
thin dusky laminated matter is sometimes interposed between the 
two masses, whereby a good parting is formed. 
Besides these partings of one stratum of coal from another, each 
stratum will be found disposed to part, at numerous secondary di- 
visions or partings, which run parallel to the former, but are neces- 
sarily not so visible or so strong. Other divisions or lines of 
separation occur, which cross the former horizontal ones in nearly a 
perpendicular direction ; these are called backs. These are crossed 
too by others, at right angles, also in a direction approaching to per- 
pendicular ; these are called cutters. The facility of separation at 
these lesser lines of partings will often be found to be promoted by a 
film of pyritous, earthy, and even stony matter having formed the 
substance which is interposed at these partings. 
In the parting between the superior part of the mass of coal, 
and the impending stratum or roof of the mine, very considerable 
differences occur. Sometimes the parting is very difficult and ba , 
from the closeness of their union. At other times the head of t e 
mass is sprinkled with a powder like soot, or powdered charcoa . 
VOL. I. ^ 
