292 On the Physical Geology of the United States, &c. 
The evidences that the periods of variation in the angular ve- 
locity of the earth were paroxysmal are threefold, viz. 
1st. The strata of sedimentary rocks show alternations of strata, 
entirely different in composition and texture, lying directly con- 
tiguous upon each other, with no intermediate blending of their 
materials ; as for example, a bed of fine slate or of limestone, 
which must have been formed in nearly tranquil water, is imme- 
diately succeeded by a coarse sandstone or aconglomerate, which 
- must have required a strong current to transport its fragments, 
and currents of variable velocities would be a necessary result of 
paroxysmal changes in the volume of the earth. 
2d. Local examples have been observed where the strata that 
had been formed up to a certain period, (as, for example, that of 
the Helderberg limestone,) have been broken up and turned on 
their edges over a large area; and succeeding this, a period of 
repose supervened, during which rocks were deposited in nearly 
horizontal strata unconformably on the upturned edges of those 
in the disturbed district, while the same strata were deposited 
conformably in the adjoining undisturbed districts, with no rocks 
of intermediate age intervening. In both cases the rocks are of 
the same kinds, have the same characters, and contain the same 
fossils. ;e a 
3d. The folded axes of the mountain chains of the eastern 
parts of the Uuited States, in which the strata have been eleva- 
ted in wrinkles and folds, all of which, when elevated at a high 
angle, have fallen over in a westward direction, giving an east- 
wardly dip. Paroxysmal elevation and the action of inertia, of- 
fer a satisfactory explanation of the folded axes and eastwardly 
dip. Had the elevation been secular, like that of the coast of 
Sweden, (where it has been perceptible only in a long course of 
years until in 1843, when there was a sudden though moderate 
elevation,) the difference in the linear velocities at the different 
distances to which the masses were elevated in the course of ages, 
would be too small to cause the inertia to produce any sensible 
effects ; but in the other case, suppose the sudden elevation of a 
mountain mass one mile in height, or more distant from the axis 
of rotation than it was before its elevation. It would still retain 
the linear velocity it had when a mile nearer the axis of rotation, 
while the proper linear velocity at this increased distance would 
3141 
be 24 miles, or 694 feet greater per hour, than that which it 
