Prof. C. Lloyd Morgan—Elevation and Subsidence. 291 
The first specimen described also showed that the shorter side was 
that on which the ribs were wide and flexuous. These facts suggest 
that the flexuous or undulating character of the ribs and furrows 
may have been induced by a pressure which acted on the living 
plant and caused it to bend; this would have the effect of widening 
and crumpling the ribs on the concave side of the bent plant. 
I].—ELevation anp SupstpENcE: A SvuGGESTION. 
By Professor C. Luoyp Morean, F.G.S., 
Of University College, Bristol. 
T is unnecessary for me to remind the readers of the GroLocicaL 
Magazine of the evidence for elevation and subsidence. For 
my present purpose it is sufficient to remind them that such elevation 
and subsidence has been attributed (1) to lateral pressure giving 
rise to long geo-anticlines and geo-synclines; (2) to expansion 
and contraction of the underlayers resulting from a rise or a fall of 
temperature ; and (8) to the loading and unloading of the areas of 
the earth’s crust affected. Apparent elevation and subsidence, which 
we may here neglect, may be due to arise or fall of the sea-level 
such as is dealt with by Prof. Hull in a recent communication to this 
MAGAZINE. 
(1.) There can be no doubt that the formation of long geo-clines 
under the influence of lateral pressure (whether produced by secular 
contraction, by the screwing of the earth’s crust suggested by George 
Darwin, or otherwise) is a factor in the upheaval and depression of 
the land. So far as my present purpose is concerned, however, it is 
only necessary to point out that during the formation of geo-clines 
under the influences of this lateral pressure there must be a tendency 
to lessen the vertical pressure on the underlayers beneath a geo- 
anticline and to increase the pressure on the underlayers beneath a 
geo-syncline. 
(2.) The effects of hydrothermal action on the solid underlayers 
of the earth’s crust would seem to be of two kinds with opposite 
tendencies. First there is the direct effect of heat with a tendency 
to expansion. Mr. Mellard Reade has lately (‘‘ Origin of Mountain 
Ranges ”’) insisted on the importance of this factor in the upheaval 
of the surface. Secondly, there are the metamorphic changes super- 
induced. The tendency of these is towards condensation or con- 
traction. Which tendency predominates? I doubt if this question 
can be answered @ priori. But we are taught that continued sedi- 
mentation involves a rise of the isogeotherms beneath the area in 
which sedimentation is taking place: and we know that there is 
abundant geological evidence that areas of sedimentation are also 
areas of subsidence. If, therefore, the changes in the solid under- 
layers which result from hydrothermal action take place pari passu 
with sedimentation, such evidence as we possess is in favour rather of 
contraction than expansion. Or if expansion does take place, its 
effects must be over-mastered by those of some opposing tendency 
or tendencies. Mr. Mellard Reade would indeed contend that the 
