36 The Low Metamorphism of the Elland Flags. 
At this point the Elland Flags consist of a series of 
sandstones, flagstones, shales and mudstones, and the beds 
can be conveniently compared with regard to the effect of 
the minor fracture upon them. There are three sandstone 
beds ; the top one is a soft, even-grained rock ; the bottom one 
is a hard even -grained sandstone ; while the third is a coarse, 
tough, ferruginous rock. The upper and lower beds have 
been ground up considerably and reduced to either sand or 
gravel, but, in the latter case, the fragments have been 
cemented together by limonite, which has been brought down 
by waters percolating through the ferruginous rocks above, 
and the result is a breccia with a limonite cement. The 
tough sandstone still remains compact near the fault, although 
it has been oxidised and has lost its toughness. 
Two beds of mudstone are exposed in the quarry ; one is 
a tough, laminated, micaceous rock, while the other is very 
similar except that it contains a high percentage of carbona- 
ceous matter. In neither case have the rocks been shattered, 
but they show considerable carbonisation. The carbonaceous 
shales have merely been shattered. 
Near to the fracture the mudstones and shales have been 
dragged down and are bent, although in the case of the shales 
this is masked by the shattering action. This is not noticeable 
in the sandstones, which either slipped down as solid blocks 
or crumpled up without bending. The resistance to com- 
pression of a number of these beds was determined with 
the following results : — 
Pounds per square inch. 
Tough Sandstone ... ... ... 2,700 
Upper Sandstone ... ... ... 720 
Bottom Sandstone ... ... ... 2,540 
Carbonaceous Shale ... ... ... 105 
Grey Shaly Mudstone ... ... ... 1,585 
Although the Tough Sandstone has not been fractured, 
the Bottom Sandstone has been considerably crushed and it 
appears that the pressure exerted on the beds by this fracture 
was in the neighbourhood of 2,600 pounds per square inch. 
This was quite sufficient, but did not crush the Grey Shaly 
Mudstone. This is explained by the fact that the mudstone 
was capable of bending and this bed has bent to the extent of 
4J deg. per inch. The flexibility of the mudstone is due to 
the high percentage of mica and to the lamination, which 
allowed the laminae to slide over each other and shear. The 
effect of the shearing has been a development of slickensiding 
along the planes of lamination and a drawing out of the 
particles. 
The Naturalist 
