DIASTROPHISM AND THE FORMATIVE PROCESSES 587 
phism and probably the basal effects were undulatory. The glacier- 
like rock mass in being thrust by its own internal stresses over 
these undulatory shear planes—in effect an undulatory floor like 
that of the glacier—must probably have gently swelled and sagged 
as does ice under similar conditions. The sea, or any other water- 
body, lying upon this creeping undulating sheet would suffer 
shiftings of outline, changes of deposition, rises and removals of 
barriers, attended by variations of faunal development. While these 
might rise to some moment, and might seem to be epeirogenic in 
nature, they would not usually suspend the main progress of sea- 
transgression, but rather, on the whole, be tributary to it, whatever 
their temporary or local effect might be. If this source of minor 
oscillations shall ultimately find warrant, it will relieve us of referring 
these various slight intercurrent undulations of the surface to those 
deep-seated potent agencies whose normal action is refractory 
rather than compliant with the gradational agencies on whose 
well-adjusted action the development of the great stratigraphic 
terranes, as a whole, are dependent. 
