W. J. McGee—Dynamnical Geology. 495 
it is evident that all such movements belong to the consequent class 
as above defined, and hence that the hypothesis utterly fails as an 
explanation of the antecedent deformation by which active geologic 
processes were initiated early in the history of the earth, and by 
which these processes have ever since been maintained. It cannot 
be too strongly emphasized that without continents zones of deposition 
could not be formed, and that continents could not come into being 
without antecedent deformation. The case is simple. Hither (1) the 
primaval earth was highly rugose, and gradation and consequent 
deformation have always been employed in reducing the rugosity, or 
else (2) a general deforming force of unknown cause and value has 
always been in operation—either the earth is a clock once wound 
up and ever since running down, or it is a prime motor whose 
mechanism may be obscure, but whose energy is ever renewed 
within itself. To the working geologist, constrained by the in- 
exorable logic of facts, there is but one choice between these 
alternatives; the Palzeozoic earth, at least, was less rugose than the 
present, and although diastatic activity has varied, it has not declined 
with the ages; and the grander earth-movements are in progress 
to-day as proved by a score of examples of continental oscillation, 
and is perhaps as active now as at any time in the past. 
So the processes by which heteromorphism of the globe are pro- 
duced (deformation and vulcanism combined) comprise (1) move- 
ments antecedent to gradational transfer of matter, predominantly 
epeirogenic, or continent-making, and predominantly diastatic, for 
which adequate cause is not yet assigned ; and (2) movements conse- 
quent upon gradational transfer of matter, predominantly orogenic, 
or mountain-making, and both diastatic and volcanic. It is impor- 
tant to discriminate these classes of movements. 
in the hypothesis. Lines of sedimentation are the margins of continents, and the 
sediments are laid down not upon horizontal surfaces, but upon seawardly sloping 
bottoms; so the sediments do not form horizontal beds, but take a variable seaward 
slope determined by marine currents, wave action, etc. Thus the mass of sediments 
is collectively in the condition of a mass of snow upon a roof or upon a mountain 
side, 7.e. in a condition of potential instability or ineguipotentiality. If the mass 
is stable in either case, it is because the friction among the particles exceeds the 
attraction of gravitation upon the particles; it is obvious thatif particle friction 
were reduced by augmentation of temperature or by alteration of constitution, or if 
the efficiency of gravitation were increased by addition to the mass, the point of 
stability might be passed, when the mass would move in the direction of the slope ; 
and it is equally obvious that if an inequipotential mass expand, the resulting move- 
ment will not take place equally in all directions, but mainly or wholly in the 
direction of least resistance, which is that of the slope. Since the sediments fringing 
continents are in a condition of inequipotentiality, any movement due to the rise of 
isogeotherms or other cause must take place in a single direction ; and it might not 
be limited to that due to expansion, for other factors co-operate. Supplemented by 
this additional conception, the hypothesis of mountain growth so ably advocated by 
Herschel, Babbage, Hall, Dana, Le Conte, Reade, and a score of others, appears to 
gain much in acceptability. 
