found that they will be thrown up again as much by one slip, as 
they appear to have been thrown down by the other. It sometimes 
happens that all the slips are down-slips, the strata seeming to have 
sunk lower in each succeeding slip. These slips differ very much 
in their width, as well as in the matter with which they appear to 
have been filled. Some, which are wide, are filled with adventi- 
tious and heterogeneous matters ; and others with soft argillaceous 
substances. Other slips are seen, in which, although the strata are 
thrown a great many fathoms off the ordinary level, the two sides 
of the fissure are found, in some places, quite close together. In 
these perpendicular fissures, or rake veins, as they are called by 
miners, a confused mass of heterogeneous matter, solid whin-stone, 
spar, ores, and metals, and particularly sulphurets of metals, are 
frequently found; very large ribs of spar, and of pyidtes, being 
very frequently thus disposed. A dyke is a separation or chasm 
in the coal and accompanying strata, which differs from the slip, 
chiefly in bearing the marks of a mere fissure or separation; the 
coal seams and other strata being not thrown off their levels, as in 
slips; and the heterogeneous matters with which the chasm has 
been filled, bearing more plainly the marks of having been brought 
there by water. 
In slips the coal metals have a vise, which is the vestigia of the 
coal, and which leads upwards, or downwards, to the separated 
stratum of coal ; but in dykes there is no such vise leading through 
to the other side. Sometimes the crack or chasm in the coal, and 
in the accompanying strata, resembles the dyke in every respect, 
except that the foreign matter is not indurated as in that of the 
dyke, but always continues loose, and generally very wet. These 
are called galls, or gashes. 
When the separation is not very considerable, and the strata on 
each side the fissure maintain their original position, it is called 
A HITCH. In some places, without any apparent cause, the coal 
