J. G. Goodchild—On “ Joints.’’ 403 
highly-disturbed and complicated zone of Paleozoic strata associated 
with the Pennine Faults. After testing the validity of this explana- 
tion by the facts coming under my notice in the course of quite nine 
more years’ work among rock of the same nature, and by the study 
of an extensive series of photographs illustrative of rock structure 
of other districts I have not been able to visit, ] may now venture 
to offer those views for wider consideration as a contribution towards 
the discussion that will be needed before the question can be deemed 
to be finally settled. 
The consolidation of rocks, as a rule, is largely dependent upon 
pressure induced by the accumulation of superincumbent strata: 
where there is reason for believing that no great thickness of over- 
lying strata has been deposited, strata otherwise favourably con- 
stituted for consolidation remain very little more compacted than at 
the time of their deposition. The Chalk of the South-east of Hng- 
land may be compared with calcareous rocks elsewhere, as an illus- 
tration of this point. Or the Tertiary sands of the same area may 
be compared under the same aspect with beds of similar origin that 
can be shown to have been at some time or other carried down 
nearer to the centre of the earth. Any such depression of strata, 
whether beneath an accumulation of superincumbent sediment or 
beneath merely the waters of the sea, involves a certain amount of 
lateral compression resulting from the rock having to adapt its 
dimensions to the smaller space. In the cases where this sideway 
squeezing of the newly formed rocks takes place under conditions of 
pressure equal in amount to those caused by the weight above, so that 
the force of the thrust exerted upon the mass would be about equal 
in every direction, the rock would be merely reduced in bulk with- 
out being much affected in other ways. But where the depression 
of the strata represents a downward phase of a great undulatory 
movement of the earth’s crust, uniformity of pressure in every direc- 
tion must be the exception rather than the rule, and the mass would 
be compressed with greatest force in directions normal to the bounding 
lines of the area affected by depression during each downward phase 
of undulation. 
Sediment consolidated under such condition could hardly escape 
being affected by a kind of inchoate cleavage or ‘bate’ varying in 
character with the nature of the sediment itself and with the extent 
and direction of the compressing forces. 
In time, another phase of terrestrial undulation reaches the depressed 
area, and the downward movement by degrees gives place to a move- 
ment in the opposite direction. The former condition of things is 
then reversed. The rocks that had been squeezed into dimensions 
less than they originally occupied, and had been solidified within 
these smaller dimensions, are now, as they return towards the 
surface, subjected to lateral strain equal in intensity, and often also 
identical in direction with the thrust exerted upon them as they 
underwent depression. In other words, they were stretched out 
sideways as much on their way up as they were squeezed in sideways 
on their way down. Where the separate laminz were so constituted 
