New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1872-06-26
GLACIAL PHENOMENA.
DEDUCTIONS FROM DISCOVERIES BY PROF
AGASSIZ

|
| SUPERINTENDENT OF THE COAST SURVEY.
U. s. STEAMER HAssLER, CoSCEPGoN BAY,
June lsince sent my first report concerning ertics
| in the Southern Temperate Zone, have been much
engrossed with this subject and have turned my aten
ton chiefly that way leaving TO Pourtas the supern
tendence Of the dredging and TO stendachper and Blake
the OF the GEOLOGICAL specimens.
On the eastern Of Patagonia had httlc oppor
tunity Of adding the information had already OBJ
tanned at Monteydeo. 1t not till We put into San
Matthias Bay for repairs that could gather few
facts. This bay is particularly interesting because
there compare the position OF the tertiary beds
in the cliffs bordering the Atlantic with that Of similar
beds in the cliffs along the northern shore Of the bay.
The southern exposure OF the latter runs for nearly
hundred miles at abOut right angles with the
| In both the Outcrops Of the beds
| nearly parallel with the surface Of the sea,
that whatever may have been their changes OF level
with reference TO the ocean, they still retain the hor
zontal position In which they deposited. I'll OF
the utmost importance to remember this point when
considering the distribution OF the erracs this part
OF the country with reference the agency that may
have transported them to their present restngplace.
Among these tertiary deposits welmarked banks OF
colossal oysters OF considerable extent OF which
ncdes with the level Of low water while another stands
at least rs feet higher The difference Of level between
these great beds of oysters Is considerable
to suggest subsistence OF the bottom during the
deposition Of the tertiary beds Higher up there
other layers full smaller fossssome about TO- others
about 20 feet above the second oyserbed The oyster
beds perfectly parallel with another. and
separated by thin layers clay and sand And So also,
the upper tertiary beds containing the smaller fossils
Among these bank consists entirely of large
numbers Of species OF scuella with single perioraton
in the posteror interambulacral area. This bank Is
particularly well marked. bank OF hard sand higher
up is also conspicuous and is another Of hard clay
standing about 100 feet above the sea line.
THE TERRACES OF PATAGONIA.
As we shall see hereafter, and Darwin has already
stated these tertiary beds extend all eastern Psa-
gona, including the Straits of Magellan Sandy
Point In consequence of dntegraton the harder beds
form as many retreating shelves like stairs, upon the
slope Of the shore bank Wherever surface denudaon
has taken place these shelves give rise to terraces
stretching horizontally at various nights all the
plains Of Patagonia. The scenery at Cliff End reminded
me somewhat Of Gay Head and its tertiary formation,
except that the upper part OF the ClR con-
sisted chiefly Of sandy clays, alternating
with which are two distinct horizontal beds q
considerable thickness. formed entirely of pebbles,
rather small and uniform in size. These pebbles vary
from the dimensions of pea hazenut to that OF
the fist more but there powders OF large faG
mens OF rock among them ut is noteworthy that While
these pebbles alternate I'm regular stratcation the
sandy clays in the upper part of the cliff they also
upon the shelves below. In the latter case, however
they form only superficial deposits and DO penetrate
with the beds which they the interior of the
strata. 1t has occurred that similar superficial
accumulatons Of pebbles upon the shelves bordering
the bed OF the Santa Cruz River may have been
mistaken by Darwin for indications of successive
upheavals. 1t Is certain that there are no
beaches here, marking successive steps OF tho uphcay
OF the country What Darwin has considered evil
denee gradual rise OF the shore the denGded
OF the horizontal tertiary deposits which every
where form parallel terraces As for my self see here
evidence OF upheayal except the level of the fossil
beds OF oysters and other fossils in the tertiary beds
above the water, and the presence OF fresh shells OF y
ing species upon and above the shore banks. These,
however, only indicate that upheaya has taken place
since the deposition Of the tertiaIies, and
while the shells living already existed.
without pointing to the rise by successive steps. SIN
appear that the country has been sub
merged during the TanspOsOn OF the erraties Toward
end OF San Matthias Bay, at Port San Antonio
where extensive foundations have taken place tho
very formations here described, these same pebbles
occur again. But at Port San Antonio instead Of
being well defined, continuous horizontal beds,
above the sea-eyel, they shore peb
bles covering ia deep layer the whole
extent OF the beach the inequality OF which they follow.
Their position here shows beyond the possibility Of
doubt that the whole set Of beds above which they rest
in regular qualification Ch End has been completely
broken and recently removed by tic action Of the
sea- and the pebbles themselves thus brought 10 the
level or course It follows that these pcbD have not
been ground upon the modern beach, but upon Older
foundation corresponding at the time 20 the level at
which the pebble beds now stand at Clh End
THE EVIDENCES OF GLACIAL ACTION.
SO far the facts. inclined TO add inference
from subsequent observations made further SOUTH the
relation Of which the facts above stated TO
clear that these pebbles have passed through the mill
of glaciers bottom before they worked by tho
floods INTO present position in the beds OF Cliff End
and upon the beach Of San Antonio and do
the floods which formed these foundations could not as
81 III COTS aa tho
close Of the glacial period, the result OF change
of level between land and sea- AS soon as eeolo-
gists have learned 10 appreciate the extent to
which our globe has been covered and fashioned
by ice, they may be less inclined TO advocate
changes level between land and wherever they
meet with evidence Of the action Of water especially
where no marine remains Of any kind mark the pres
enee OF the AS have already said the small and
remarkably uniform size Of the pebbles In Port
tonic particularly noticeable. and also the fact that
none hard rocks indeed only the very hardest kind
OF rocks, are represented among them. Por
which I will explain presently, I would mention
especially pebbles of red porphyry, and others OF
green compact epdote, common In this formation.
The position of the Bay OF San Matthias its great length,
and particularly the depression deDudation at
Port Antonio suggest the probability that the Rio
Negro poured its waters into this large gulf instead
opening directly into the should add that
while erratic pebbles in such abundance az Ban
Matthias Bay, there bard rocks IN place upon
which peculiar marks OF glacial action could be per-
eeived. Nor would these stratined banks Of pebbles,
even though unquestonably connected with the drift,
afford in themselves any unmistakabe evidence gla-
cal derivation.
As time and the circumstances Of vessel obliged
me renounce the hope had cherished Of seeing at
least the and the shore bluffs Of the Negro
Santa Cruz. and Gaagos Rivers and also Of Writing the
Fakands, could not connect my observations In San
Matthias Bay with any other facts on the eastern
NJ PAN tts oufv slanda Ru1a aft