The Portland daily press., 1873-08-25
BY PROF. C. H. HITCHCOCK.

[Read before the American Association
In obedience to the custom of present.
ing sketch of the local geology at the
meetings of the Association, have made
some special examination of the rocks
about Portland.
The earliest sketch of the geology of
this neighborhood was published by my
father, the late President Edward Hi.ch-
Geek. in the Journal of The Boston Society
of Natural History, Vol. 1. 1886, from
observations made the previous year. He
called the clays Tertiary, and was the
first to describe the shell afterwards fa-
nous, NuculG Portlaadicd, for long time
believed to be extinct. Mr.. G. II. Jackson
also made few illusions TO the geology
of Portland in his Geological Survey.
am not aware of any other publica-
tions before my report as State Geologist
of Maine in 1862. In that report il is
stated that evidence exists for regarding
Portland clays and sands as covered by
ce-drift, at least in part; but | did not
commit myself to this view, not having
examined the deposits critically and sys-
tematcally. This view was upheld by
my predecessors, in the use of the word
Tertiary, by the unanimous belief OF the
officers Of the Portland Society of Natural
History, who lived on the ground, and by
the confident assurances OF A. s. Packard,
Jr.. then assistant on the scientific survey.
One of most thorough memoirs relating to
the geology of the surface deposits of this
neighborhood, appeared In the first vol
ume of the memoirs of the Boston Society
of Natural History in 1865, by DIR. A. S.
Packard, Jr., of Salem, entitled "Observa-
tions on the Glacial Phenomena of Labra-
dor and Maine." He describes minutely
all the localities in Maine where the fussils
had been found in the clay, and present.
ed interesting geEeraliZations respecting
| the history of the entire Post-rertiary
| Period. This paper will for long time
| continue to be the great authority upon
these subjects for this part of the world.
find also that DIR. Il. Sterry Hunt has In
some recent publications referred to the tai
cOse and micaceous rocks about Portland.
He believes they are to be referred to the
Huronian, and that they are older than
the White Mountain gneisses adjacent
in Deering, Gorham, &c., because
the gneisses along the Grand Trunk rail-
way in Maine have low dips, while the
green schists are commonly highly inclined
| Even If the dip of the gneiss could be in
variably established as lower, l should
| conclude that it was formed, metamor-
phosed and elevated before the origin of
the Huronan system, and at the later Pc
|
easily moulded, were forced into more
| vertical position. ! do not find the two
rocks in contact in the White Mountains.
| My general theory of the structure is the
| following. The green schists were depos-
| tied in basin of gneiss, now embraced
| between Harpswell and Saco river, in one
| direction, and between Decring and West
| brook and some ancient river fifteen or
twenty miles out TO sea. Originally these
talcose rocks may have extended fifty
or sixty miles out to sea, and the force of
elevation has crowded the outer rim of
gneiss towards the interior, pushing up the
schsts into highly inclined position.
Supposing that Halfway Rock is gneiss,
we have in that and the similar rocks of
| the Isles of Shoals, relics OF the outer rim
| which borders the Huronian rocks on their
| ocean side. Before the submergence of
| the Gulf of Maine, this ridge must have
been prominent. The gneiss occupies
| position along the shore from GOrham to
| beyond the Penobscot river, while the
! Hurunian series is limited to Portland, and
| the towns east of the Ssco river.
This view'of the stratigraphical relations
| of the rocks in this region, is derived from
| personal explorations this season, in con-
| necton with five years work on similar
| formations in New Hampshire.
The strata of the Huronian system in
| Cape Elizabeth stand everywhere nearly
| upon their edges, so that their contents
can be perceived by examining
the surface. At Great Pond,
the plumbaginons states have, in
early times, been dug into with the expec-
tation of finding coal, and l understand
that some have imagined that coal can
now be mined In that neighborhood. It
must be stated plainly, for the benefit of
such persons, that exploration for coal in
quantity, in this vicinity, will he entirely
futile, and is furthermore needless, since
if any veins existed they would appear on
the surface.
GENERAL CONCLUSIONS.
The solid rocks are referred to the
Upper Laurentian and Huronian systems,
or the MeIamorphic Quebec group of
| Logan. The earthly deposits are referred
altogether 10 Alluvium-there is no Ter
| tiary-and the clays are all above the
| glacial drift, corresponding with the de-
posits Of the Champlain period in other
! parts of the continent.
POST TERTIARY DEPOSITS.
have already indicated the opinion of
| my predecessors upon the matter of the
succession of the Post Tertiary deposits.
Recent examination has led me to as
sign different order to them from that
referred to, and think all will admit that
the evidence is satisfactory.
The succession, as | read the strata, is
as follows:
l. The covering of this city and the
| whole surrounding country with an I'M
mense sheet of ice, which pushed towards
| the ocean, transporting boulders ana
| fragments of rock, rounding, scratching
and polishing the ledges, or the Glacier
| Period.
.. A period of submergence to the depth
! of forty or fifty feet, in which arctic
mollusks inhabiiing the deep waters, say
| 200 feet, located themselves upon the very
| spot where we now stand. This is the
( period of the Leda Clay.
8. Sands contaiDg shells of animals liy-
| ing on the sea shore, the highest of them
about 100 feet above tide water. This is
the Sa1icaua Period
proposed in 1861 the name of Cham
| plain Period for the combination of the
two just mentioned,-a term which has
generally been adopted by American
geologists. first saw the distinction of
lower and upper in the writings of Prof.
| G. B. Adams in Second Annual Report
upon the Geology of Vermont in 1865.
The names Leda clay and Saxcava
sands were proposed for the subdivisions
by DR.. Dawson of McGill College, Mon
treal, an honored associate who has dis
couraged all other collectors of these
Champlain fossils by the enormous num-
Der of species which he has discovered.
He has more than donbled the hsts dc
given by all previous observers