DIASTROPHISM AND THE FORMATIVE PROCESSES — 531 
proposition that the ordinary diastrophism of the earth 1s not suited to 
give the shallow-water seas which the geologic record so abundantly 
presents for inter pretation. 
If to escape the force of this proposition one indulges the 
inherited habit of assuming that a flat area from the sea-bottom 
“‘might have been”’ lifted to just the right height or let down from 
the land area to just the right level for this specific shallow sub- 
mergence, it is well to note that the right height is only a small 
fraction of the full range of height involved in deformation and that 
the chances of the close adjustment required are correspondingly 
small, and should be correspondingly infrequent as well as irregular | 
in distribution, whereas the actual case presented by the geologic 
seas is a systematic repetition of this state from period to period, 
combined with similarity of action in different continents. 
If one indulges in the familiar old idea of a slow subsidence to 
the sea-level and below, he takes refuge in the most plausible of all 
diastrophic devices for meeting the actual case. In pure theory, 
a downward diastrophic movement has little advantage over 
an upward one in meeting the demands of this case. A down- 
ward movement is, however, supplemented by gradation. It is 
commonly assumed in such a case that the deposits build up the 
sinking area as fast as it descends and thus preserve an adjustment 
to the sea-surface. Now if the rate of deposition and the rate of 
subsidence were inherently correlated with one another so as to be 
co-operative in the same phase, such an adjustment would be 
natural and be often repeated and so meet the requirements of the 
case to this extent. If,.for example, the weighting due to deposi- 
tion were sufficient to cause proportionate subsidence, the adjust- 
ment would be easily and naturally maintained when once made. 
This would happen if the earth-surface were in free isostatic adjust- 
ment to this degree of nicety and the stiffness of the crust offered no 
effective resistance to continuous warping. On the adjacent land, 
however, whence the material for the deposit is being taken, the 
unloading should cause a proportionate rise and the sea trans- 
gression be defeated. 
If, however, general elevations and subsidences are dependent 
on differential stresses in the body of a very stiff elastic earth capable 
