Staunton spectator and vindicator. [volume] (Staunton, Va.) 1896-1916, 1909-10-01
THE GROUND PLAN OF NORTH
AMERICA.

AmENxNA.
NEW PUBLICATION BY GEOLOGICAL
SURVEY.
All work done and conclusions reach
ed by biologists in regard to the olde
} rocks of the North American continen
have been summarized by G. r. Val
\ Hise, president of the University o
Wisconsin, and c. K. Leith, professo
at the same institution, in bulletil
(No. 36O) just issued by the United
States Geological Survey under the It'll,
"Pre-Cambrian geology Of North Amer
ica"
The term pre-Cambrian is used to in
clude all rocks supposed to have beer
in existence before those laid down in
the Cambrian period, at the beginning
OF the Paleozoic era. In the early days
of geologic study all these pre- Cambrian
rocks were supposed to be of igneous
origin and to record time before life on
the globe began. Later, when both
sedimentary beds and fossils were dis
covered in them, they were subdivided
usually into two variously named sys-
TENS, the older of which, now general
Unknown as the Archean, was supposed
to be destitute of life and sediments,
while the younger, now called the
Algonkian, was supposed to mark the
earliest beginning of both. More re-
Gently sediments have been found and
| fossils suspected in certain Archean
rocks and that the distinction between
these two great systems now depends
on other points of difference, most of
which are not quite SO easily grasped
or applied. Nevertheless the subdivi-
sion is useful, since the Archean and
Algonkian are separated from each !
other by great ''unconformity'' and
differ from each other physically as
much as the Algonkian differs from the
Cambrian.
Where so much doubt existed in re-
gard to even such enormous systems, it
was inevitable that greater doubt
should exist in regard to details. Many
writings on the subject have proved to
be erroneous very shortly after their
and marked inconsistencies
and disagreements still exist. The
matter in the present volume has been !
in the hope that the setting of
The ideas of all writers on the subject
'lde by side might help to clarity mat !
,ers and to show definitely the present {
state of knowledge on the subject. S
In the discussion the aim of the au- t
hors has been not to call attention TO il
what seemed erroneous, but to point
nut where there was harmony between T
he different authors, often yelled be- a
ause terms are used with different e
lgnifications; and to note the import d
mt conclusions which have been clear S
Y determined. Statements and con-
lusions with which the writers did
ot agree are in general not criticised,
or is any refutation attempted, unless y;
ne point at issue was fundamental and :
ould not be overlooked. O.
The pre-Cambrian rocks are import
MT because they are generally consid- -
red to indicate the basal architectural
satures IN the ground plan of the -,
lorth American continent. The larg- 70
st area occupies the northeastern por- o.
on OF the continent, extending north
'est, north, and northeast from Min
esota, the Great Lakes, and the st.
'aWrence to the Arctic and Atlantic th
ceans. This has been called the sspre- ao
ambrian Shield" the sLaurentian ra
ontinent,i" and the "Archean pro- ju
lxis" of North America. of
On the southeast the pre-Cambrian
Held is separated by narrow area of
ounger rocks from the pre-Cambrian
'cks OF the northern end of the Ap-
system. Considerable areas ou
egln in Newfoundland and extend tn
trough New England down the east M
n side of the Appalachian system to Pa
labama. In eastern Canada and in be
e Adirondacks of New York are out l..
ers of pre- -Cambrian rocks surrounded Oh
younger sediments, which,, while lor
ose to the Appalachian system, do PEE
It form any part of it. In western fin
nlted States pref -Cambrian rocks form by
rts OF some of the Cordilleran ranges, s
q in northern Montana and Idaho DR.
q southern British Columbia they Au
cupy very large areas. In the Mis- Nc
slppi Valley isolated areas of them
pear in Wisconsin, Minnesota, Iowa, Z
lkota, Missouri, Oklahoma, and Tex IN
The bulletin may be had free of OF
arge by applying to the Director, er
lited States Geological Survey, Wash anf