ON CR YSTALLINE AND .SLA TT GLEA VAOE. 239 
Whitish Green Slate. 
1. Percentage of iron 3.24 
2. " 3 13- 
Mean . . 3.18 
According to these analyses the quantity of iron in the 
dark slate immediately adjacent to the greenish spot is 
nearly double the quantity contained in the spot itself. 
This is about the proportion which the magnetic experi- 
ments suggested. 
Let me now remind you that the facts brought before 
you are typical each is the representative of a class. We 
have seen shells crushed, the trilobites squeezed, beds con- 
torted, nodules of greenish marl flattened; and all these 
sources of independent testimony point to one and the 
same conclusion, namely, that slate-rocks have been sub- 
jected to enormous pressure in a direction at right angles 
to the planes of cleavage. 
In reference to Mr. Sorby's contorted bed, I have said 
that by supposing it to be stretched out and its length 
measured, it would give us an idea of the amount of yield- 
ing of the mass above and below the bed. Such a measure- 
ment, however, would not give the exact amount of yield- 
ing. I hold in my hand a specimen of slate with its bed- 
ding marked upon it; the lower portions of each layer being 
composed of a comparatively coarse gritty material some- 
thing like what you may suppose the contorted bed to be 
composed of. Now, in crossing these gritty portions, the 
cleavage turns, as if tending to cross the bedding at 
another angle. When the pressure began to act, the inter- 
mediate bed, which is not entirely unyielding, suffered 
longitudinal pressure; as it bent, the pressure became 
gradually more transverse, and the direction of its cleav- 
age is exactly such as you would infer from an action of 
this kind it is neither quite across the bed, nor yet in the 
same direction as the cleavage of the slate above and below 
it, but intermediate between both. Supposing the cleav- 
age to be at right angles to the pressure, this is the 
direction which it ought to take across these more unyield- 
ing strata. 
Thus we have established the concurrence of the phenom- 
ena of cleavage and pressure that they accompany each 
other] but the question still remains. Is the pressure suffi- 
