GENERAL GEOLOGY.


itself to the contracting core. Now a very moderate loading over
a wide area accompanied by a corresponding unloading of an adja-
cent region, may be quite sufficient to determine that the burdened
area shall bend downward and the lightened area upward under the
tangential strain.  The sediments are thus conceived to be the
deciding agency rather than the effective cause of the flexure.
(orrelative Dl/icaJlties. This view explains a correlative difficulty
often overlooked. There are several instances where essentially
conformable series have a thickness of from 40,000 to 60,000 feet.
Now it is quite clear, upon consideration, that no such enormous
subsidences affected the whole continent, for either (1) it must
have been previously elevated to an altogether incredible height,
or else, (2) it would have been submerged long before the accumu-
lation was complete, and further fragmental sedimentation would
lhave been prevented for want of a source. An equally grave prob-
lem is encountered in attempting to find an adequate source for the
enormous amount of material required for such a series. If the
present Appalachian mountain range were cut down to the ocean
level and strewn over an equal area of the adjacent Atlantic bed, it
would make but a relatively trivial formation. If the entire conti-
nent of North America were worn to the sea level, it would not give
more than about twice the material of the Paleozoic sediments of
the Appalachian region, according to standard estimates. To fur-
nish the requisite material for the whole Paleozoic series of the con-
tinent, from the contracted areas then exposed, would require a most
extraordinary elevation on any hypothesis of general continental
subsidence.
If, however, the land be gradually elevated as it is unburdened
by wear, while the adjacent sea bottom correspondingly sinks under
its accumulations, these difficulties vanish, since the source of ma-
terial is continually renewed. The generalized conception is that of
the sea bottom and adjacent land surface tending to rotate about an
axis near the shore line, the former descending and the latter as-
cending. This conception is supported by stratigraphical evidence
throughout geological history, subject, however, to occasional pro-
found intercurrent general revolutions.
WCas there Life ? The interesting question arises, Was the earth
graced. during this era, with either animal or vegetable life? So
far as the formation in Wisconsin has thus far been questioned, it
has returned no direct answer. Not only have no fossil remains
been found, but no organic products such as limestone and graphite,
which are thought to indicate the presence of life. But this evi-