368 
the forms of the corrugations would be of the above general 
character, and that they would not consist of long-phased 
rolling undulations with flattened anticlinals, but rather of 
cusp-like elevated ridges, with lateral profiles somewhat cir- 
cular. The horizontal pressure, though not actually evanescent, 
would be small at the highest, and greatest at the lowest points 
of the corrugations. 
The radius of the curves which define the sides of the 
elevations, as given by the above expression, being constant, 
any additional lateral compression could not be met by an 
increase in the curvature of the corrugations; so that there 
would be a tendency to accumulate material about the anti- 
clinals. This circumstance would account for the plications 
observed on the flanks of mountain-ranges. For the tendency 
to heap the material together in such situations would be met 
by its descending superficially by its own weight, until it 
attained the angle of repose, and in so doing the strata would 
become plicated. Such seems a more probable account of the 
plications, which are often on quite a small scale, than that 
they have been formed directly by the general compression 
of the crust. | 
Causes were suggested which might tend to lessen the 
compression in the neighbourhood of anticlinals, and admit of 
the extrusion of steam and lava from below. In connection 
with this point it was argued that the permanent state of 
fusion of the lava in certain volcanic vents, such as Stromboli 
and Kilauea, can be due to nothing else than the passage of 
intensely heated vapours through them; whence it would 
follow that any place in the earth’s crust, which is not suffi- 
ciently firmly constituted to prevent the passage of steam at 
a high tension, might be sufficient to originate a volcano. 
It was admitted that the larger features of continental 
plateaux and oceanic depressions had been so far left unex- 
plained. 
