834 REPORT—1885. 
pensed with. For cutting across a block in a direction parallel to the 
‘end,’ a circular saw worked by steam is employed in the larger quarries, 
and when the operation is performed by hand it requires much more care 
than cutting in the other direction. The method employed is to cut and 
carefully smooth a groove in one ‘side’ of the block, then turn it over and 
strike a heavy blow with a mallet upon the opposite point of the other 
‘side.’ Ifthe ‘side’ is smooth and perpendicular to the cleavage-face, a 
cut may be started with a chisel instead of the groove, but for a block 
whose ‘sides’ are ‘bevel’ the method described above must be adopted. 
Again, in splitting the blocks into slates, the splitis always effected 
from ‘end’ to ‘end,’ because it is thus less liable to ‘run out’ across 
the cleavage than if the operation were attempted from the ‘side.’ There 
are, however, in some parts of North Wales certain ‘ veins’ or beds of 
slate which can be cleaved from the ‘side.’ In this case, too, the blocks 
can be cut across by the same process as that described for cutting them 
lengthwise. Such ‘veins’ are said by the quarrymen to have ‘no 
length and breadth,’ and we may suppose that in them the strain ellipsoid 
is one of rotation, as in Professor Haughton’s calculations. Certain beds 
of slate which are rather coarse-grained at the bottom and grow finer up- 
wards, must be split always from the top ‘end’; such is the case in some 
of the Ffestiniog veins. 
The fine strize seen on the surface of a slate, and regarded by Mr. 
Fisher! as an arrangement analogous to ‘craig and tail,’ connected with 
the shearing movement of the rock-mass, seem, however, to be dependent 
less on the ‘grain’ than on the method of splitting the rock into slates. 
When a block has been roughly split off by a blow upon a chisel applied 
at the end, it is seen that the striz are not straight and parallel, but 
diverge in curves from the point of percussion, and sometimes from 
harder lumps or bands in the slate. This appearance is not observable 
in a slate split in the ordinary way, for the cleavage is opened by two 
broad chisels inserted at the end, and the resulting surface shows there- 
fore a system of roughly straight and parallel striz, as may be well seen 
on wetting a cleavage-face of an ordinary roofing-slate. 
The mode of splitting a block into slates also illustrates the internal 
structure of the rock. A block is taken of sufficient thickness to yield 
say eight slates ; this is split into two ‘fours,’ each of these into two ‘ twos,’ 
and finally each of the latter into two slates. In this last stage of the 
process there is a tendency for the split to ‘run out’ to the face of the 
slate on the weaker side. Accordingly, after starting the split at one 
‘end’ by two broad chisels driven in with a hammer, the workman 
watches its progress carefully, and on seeing it deviate from the true 
cleavage, he draws it back by slightly bending the stronger half. This 
tendency of the split to ‘run out’ is strongest in the harder ‘ veins’ or 
beds and in blocks which have been indurated by proximity to a dyke (a 
peculiarity known as hollt gron, or ‘round cleavage’). In this case the 
quarryman sometimes has to mark or guide the cleavage all round the 
edge before beginning to open it, especially in cleaving the thickness of 
two slates. In the softer beds, on the other hand, there is a liability to 
break in the process of splitting, and the workman is sometimes obliged 
to use a long flat chisel, or ‘driver,’ which he forces into the split with 
a mallet. 
‘he successful splitting of the slate-rock depends on its possessing a 
1 Geol. Mag., 1884, p. 269. 
