New method of estimating the age of Niagara Falls

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NEW METHOD OF ESTIMATING THE AGE
OF NIAGARA FALLS

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75

1899

NEW METHOD

OF ESTIMATIXG THE AGE

OF NIAGARA FALLS

BY

G. FREDERICK WRIGHT

REPRINTED FROM APPLETONft' POPULAR SCIENCE MONTHLY
FOR JUXE, 1899

NEW YORK

D. APPLETON AND COMPANY

1899

216818

NEW METHOD

OF ESTIMATING THE AGE

OF NIAGARA FALLS

BY

G. FREDEEICK WRIGHT

REPRINTED FROM APPLET OXS' POPULAR SCIENCE MONTHLY
FOR JUNE, 189U

NEW YORK
D. APPLETON AND COMPANY

1899

Copyright, 1899,
By D. APPLETON and COMPANY.

NEW METilUD OF ESTIMATING
THE AGE OF NIAGARA FALLS. •

BOTH the interest and the importance of the subject make it
worth while to follow out every clew that may lead to the ap-
proximate determination of the age of Niagara Falls. During this
past season, in connection with some work done for the New York
Central Railroad upon their branch line which runs along the eastern
face of the gorge from Bloody Run to Lewiston, I fortunately came
into possession of data from which an estimate of the age of the falls
can be made entirely independent of those which have heretofore
been current. The bearing and importance of the new data can best
be seen after a brief resume of the efforts heretofore made to solve
this important problem.

In 1841 Sir Charles Lyell and the late Prof. James Hall visited
the falls together; but, having no means of determining the rate
of recession, except from the indefinite reports of residents and guides,
they could place no great confidence in the " guess," made by Sir
Charles Lyell, that it could not be more than one foot a year. As
the length of the gorge from Lewiston up is about seven miles, the
time required for its erosion at this rate would be thirty-five thousand
years. The great authority and popularity of Lyell led the general
public to put more confidence in this estimate than the distinguished
authors themselves did. Mr. Bakewell, another eminent English
geologist, at about the same time estimated the rate of the recession
as threefold greater than Lyell and Hall had done, which would re-
duce the time to about eleven thousand years.

But, to prepare the way for a more definite settlement of the
question, the New Yoyk. Geological Survey, under Professor Hall's
direction, had a careful trigonometric survey of the Horseshoe Fall
made in 1842, erecting monuments at the points at which their angles
were taken, so that, after a sufficient lapse of time, the actual rate

2 ESTIMATING THE AGE OF NIAGARA FALLS.

of recession could be more accurately determined. In 18S6 Mr.
Woodward, of the United States Geological Survey, made a new
survey, and found that the actual amount of recession in the center

Fig. 1. — Looking north I'rom below the Wliirlpool, showiuir the electric road at the bottom
of the east side of the gorge, and the steam road descending the face about lialfway to
the top.

of the Horseshoe Fall had proceeded at an average rate of about five
feet per annum. The subject was thoroughly discussed by Drs.
Pohlman and Gilbert, at the Buffalo meeting of the American Asso-
ciation in 1886, when it was proved, to the satisfaction of every one,
that, if the supply of water had been constant throughout its history^
the whole work of eroding the gorge from Lewiston to the Falls
would have been accomplished, at the present rate of recession, in
about seven thousand years.

But the question was immediately raised, Has the supply of water
in Niagara River been constant? It was my privilege, in the autumn
of 1892 (see Bulletin of the Geological Society of America, vol. iv,
pp. 421-427), to bring forth the first positive evidence that the water
pouring over l^iagara had for a time been diverted, having been
turned through Lake Nipissing down the valley of the Mattawa into
the Ottawa River, following nearly the line of Champ] ain's old trail
and of the present Canadian Pacific Railroad. The correctness of
this inference has been abundantly confirmed by subsequent inves-

ESTIMATING' THE JC/A' OF SlAdMiA FALLS. 3

tigations of Mr. V. W. 'YnyVn- ami Dr. lioliert licll.' 'I'lio occasion
of this diversion of the drainage of the Great Lakes from the Niagara
through the Ottawa Valley was the well-known northerly snhsidence
of the land in Canada at the close of the Glacial period. When the
ice melted off from the lower part of the Ottawa Valley the land
stood five hundred feet lower than it does now, but the extent of this
subsidence diminished both to the south and the west, making it
difficult to estimate just how great it was at the Nipissing outlet. A
subsidence of one hundred feet at that point, however, would now
divert the waters into the Ottawa River. That it actually was so
diverted is shown both by converging high-level shore lines at the
head of the Mattawa Valley and by the immense delta deposits at
its junction with the Ottawa, to which attention was first called in
my paper referred to above.

Fi(,. -1.

-\ icw looking east across the gortre near the mouth, showing the raih'oads and the
outcrops of Clinton and Is'iagara limestones above the steam road.

The indeterminate question which remained was, At what rate
did this postglacial elevation of land which has brought it up to
its present level proceed? Dr. Gilbert, Professor Spencer, and Mr.
Taylor have brought forth a variety of facts which, according to

* See article by Mr. Taylor on The Scoured Bowlders of the Mattawa Valley, in the
American Journal of Science, March, 1897, pp. 208-218.

4 ESTIMATING THE AGE OF NIAGARA FALLS.

their interpretation, show that this rate of elevation was so slow that
from twenty thousand to thirty thousand years was required to restore
to the Niagara River its present volume of water. Their arguments
are based upon the varying width and depth of the Niagara gorge,
proving, as they think, the presence of a smaller amount of water
during the erosion of some portions. Dr. Gilbert has also brought
forward some facts concerning the extent of supposed erosion pro-
duced by the diverted waters of Niagara when passing over an
intermediate outlet between Lake Simcoe and Lake Nipissing. But
the difficulty of obtaining any safe basis for calculation upon these
speculative considerations has increased the desire to find a means of
calculation which should be independent of the indeterminate prob-
lems involved. That I think I have found, and so have made a
beginning in obtaining desired results. The neiv evidence lies in
the extent of the enlargement of the mouth of the Niagara gorge at
Lewiston since the recession of the falls began.

It is evident that the oldest part of the Niagara gorge is at its
mouth, at Lewiston, where the escarpment suddenly breaks down to
the level of Lake Ontario. The walls of the gorge rise here to a
height of three hundred and forty feet above the level of the river.
It is clear that from the moment the recession of the falls began at
Lewiston the walls of the gorge on either side have been subject to
the action of constant disintegrating agencies, tending to enlarge
the mouth and make it Y-shaped. What I did last summer was to
measure the exact amount of this enlargement, and to obtain an ap-
proximate estimate of the rate at which it is going on.* As this en-
largement proceeds wholly through the action of atmospheric agen-
cies, the conditions are constant, and it is hoped that sufficiently
definite results have been obtained to set some limits to the specula-
tions which have been made upon more indefinite grounds.

The face on the east side of the gorge presents a series of alternate
layers of hard and soft rocks, of which certain portions are very sus-
ceptible to the disintegrating agencies of the atmosphere. The sum-
mit consists of from twenty to thirty feet of compact Niagara lime-
stone, which is underlaid by about seventy feet of Niagara shale;
which in turn rests upon a compact stratmn of Clinton limestone
about twenty feet thick, which again is underlaid by a slialy deposit
of seventy feet, resting upon a compact stratum of Medina sandstone
twenty feet thick, below which a softer sandstone, that crumbles
somewhat readily, extends to the level of the river.

* For opportunity to do this work I am indebted to the interest of President S. R.

Callaway, of the New York Central Railroad. The measurements were made by Mr. George

S. Tibbits, engineer of the western division. The photographs were taken by Mr. C. F.
Dutton, of Cleveland.

ESTIMATING THE AU E OF NIAGARA FALLS. 5

The present width of the river at the month of the gorge is
seven hundred and seventy feet. It is scarcely possible that the
original width of the gorge was here any less than this, for in the
narrowest places above, even where the Kiagara limestone is much
thicker than at Lewiston, it is nowhere much less than six hundred
feet in width. Xor is it probable that the river has to any consider-
able extent enlarged its channel at the mouth of the gorge at the
water level. On the contrary, it is more probable that the mouth
has been somewhat contracted, for the large masses of Xiagara and
Clinton limestone and Medina sandstone which have fallen down as
the shales were undermined have accunuilated at the base as a talus,

Fig. 3. — Loiikiii;r up tlie gorge from near Lewiston, sliowing on the left the exposed situation
of the eiistern face of the gorge at the extreme angle, -where the measurements were made.

which the present current of the river is too feeble to remove. This
talus of great blocks of hard stone has effectually riprapped the
banks, and really encroached to some extent upon the original
channel.

"We may therefore assume with confidence that the enlargement,
under subaerial agencies, of the mouth of the gorge at the top of
the escarpment has been no greater than the distance from the pres-
ent water's edge to the present line of the escarpment at the summit
of the ^N^iagara limestone. This ^ve found to he three hundred and
eighty-eight feet — that is, the upper stratum of hard rock on the
east side of the gorge had retreated that distance, through the action
of atmospheric agencies, since the formation of the gorge first began.
The accompanying photogravures and diagram w'ill present the facts

6 ESTIMATING THE AGE OF NIAGARA FALLS.

at a glance. The total work of enlargement on the east side of the
gorge has been the removal of an inverted triangular section of the
rock strata three hundred and forty feet high and three hundred and
eighty-eight feet base, which would be the same as a rectangular
section of one hundred and ninety-four feet base. From this one
can readily see that if the average erosion has been at the rate of
one quarter of an inch per annum, the whole amount would have
fallen down in less than ten thousand years; while if the time is
lengthened, as some would have it, to forty thousand years, the rate
would be reduced to one sixteenth of an inch per year.

Fortunately, the construction of the railroad along the face of
the eastern wall of the gorge affords opportunity to study the rate
of erosion during a definite period of time. The accompanying
photogravures will illustrate to the eye facts which it is hard to
make impressive by words alone. The course of the road is diago-
nally down the face of the gorge from its summit for a distance of
about two miles, descending in that space about two hundred feet
to the outcrop of hard quartzose Medina sandstone. The lower mile
of this exposure presents the typical situation for making an estimate
of the rate at which the face is crumbling away.

Beginning at what used to be known as the " Hermit's Cave,"
near the Catholic College grounds, where the Niagara shale is well
exposed, and extending to the outer limit of the gorge, the height
of the face above the railroad averages one hundred and fifty feet.
ISTow, the crumbling away of the superincumbent cliffs gives contin-
ual trouble to the road. Three watchmen are constantly employed
along this distance to remove the debris which falls down, and to give
warning if more comes down than they can remove before trains are
due. The seventy feet of ISTiagara shale, and the equal thickness of
shaly Medina rock which underlies the Clinton limestone, are con-
stantly falling off, even in fair weather, as any one can experience by
walking along the bank; while after storms, and especially in the
spring, when the frost is coming out, the disintegration proceeds at a
much more rapid rate. Sometimes two or three days are required by
the whole force of section hands to throw over the bank the result
of a single fall of material.

At a rate of one quarter of an inch of waste each year the amount
of debris accumulating for removal on the track along this distance
would be only six hundred and ten cubic yards per annum — that is,
if six hundred and ten cubic yards of material falls down from one
mile of the face of the wall where it is a hundred and fifty feet
high, the whole amount of enlargement of tlie mouth of the gorge
would be accomplished in less than ten thousand years. Exact ac-
counts have not been kept by the railroad; but even a hasty exami-

ESTIMATING THE Af.'E OF X/Ad A/x'.\ FALLS.

nation of the face of the wall makes it sure tliiit the actual amount
removed lias been greatly in excess of six hundred yards annually.
This estimate is based partly on the im]ir<'ssion of tlio railroad offir-jals
as to the cost of re-
moval, and partly on
the impressions of the
watchmen who sjDend
their time in keeping-
guard and in the work
of removing it.

But that is not
all. The accompany-
ing photogravures indi-
cate an actual amount
of removal over a part
of the area enormously
in excess of the rate
supposed. Fig. 5 shows
a portion of the preci-
pice, a hundred feet
high, where the road
first comes down to the
level of the Clinton
limestone, and where,
consequently, the
wholQ thickness of the
Niagara shale is acces-
sible to examination. Fortunately, Patrick Maci^amara, the w^atch-
man at this station, was a workman on the road at the time of its
construction in 1854, and has been connected with the road ever
since, having been at his present post for twelve years. "We have
therefore his distinct remembrance, as well as the appearance of
the bank, to inform us where the face of the original excavation
then was. In the picture he is standing at the original face, while
the other figure is nearly at the back of the space which has been
left empty by the crumbling away of the shale. The horizon-
tal distance is fully twenty feet, and the rocks overhang to that
amount for the whole distance exposed in the photogi'aph. All this
amount of shale has fallen down in forty-four years, making a rate
many times larger than the highest we have taken as the basis of our
estimate. Of course, this rate for the crumbling away of the Niagara
shale on its fresh exposure is much in excess of the average rate for
a long period of time; but it is clear that the rate of erosion at the
base of the Niagara limestone at the mouth of the gorge can never

Fig. 4. — Nearer \"i<.-v, -f ilir npi'.-i- |M.rti
the niou''h, showinir the oxpiisiue
that point.

ii -t tl < Cm- II' ;-r
It the situutiou at.

ESTIMATING THE AGE OF NIAGARA FALLS.

have been sufficiently slow to reduce the total average much below the
assumed rate of a quarter of an inch a year.

To impress the truth of this statement it is only necessary to fol-
low the progress, in imagination, of the crumbling process which has

Fig. 5. — Showing extent of erosion at base of the Niagara shale since ISoi.
(See description in the text.)

brought the side of the gorge to its present condition. At first the
face of the gorge was perpendicular, the plunging water making the
gorge as wide at the bottom as at the top. At successive stages the
strata of shale on the side would crumble away, as is shown in our
photograph, and undermine the strata of hard rock. The large
fragments would fall to the bottom, and, being too large to be car-
ried away by the current, would form the talus to which we have
already referred, which would grow in height with every successive
century. The actual progress of the enlargement would thus be
periodic, and not capable of measurement by decades ; but after cen-
turies the progress would be clearly marked, and especially when-
ever there was a falling away of the lower stratum of compact Medina
sandstone, which is about two hundred feet below the top, would
a new cycle of rapid disintegrations in the superincumbent strata
follow.

An important point to be noticed, and which is evident from two
of the reproduced photographs (Figs. 3 and 4), is that the talus has

ESTIMATING THE AGE OE NIAGARA EALLS. g

never reached up so high as to check the disintegration at the mouth
of the gorge of the Niagara shale and limestone which form the
upper one hundred feet of the face, and which exhibit the maximum
amount of enlargement which has taken place. The thickness of
the Niagara limestone is here so small that it has not been so im-
portant an element in forming the talus as it has been farther up the
stream, where it is two or three times as thick. Now, while our
original supposition was that one quarter of an inch annually was
eroded from the upper two hundred feet, this would involve the
erosion of a half inch per annum over the top of the gorge to bring
the calculation within the limit of ten thousand years. It certainly
is difficult for one who examines the facts upon the ground to believe
that the crumbling away of this exposed Niagara shale could have
been at any less rate than that; so that the estimate of about ten
thousand years for the date of that stage of the Glacial period in
which Niagara River first began its work of erosion at Lewiston (an

Fio. 6.— Section, drawn to equal vertical and horizontal scale, showing enlargement of Niagara
gorge on the east side at its mouth at Lewiston : 1, Niagara limestone, 20 to 30 feet ;
2, Niagara shale, 70 feet; 3, Clinton limestone, 20 to 30 feet; 4, Clinton and Medina
shale, 70 feet ; 5, Quartzose Medina sandstone, 20 to 30 feet : 6, softer Medina sandstone,
120 feet above water level.

estimate which is supported by a great variety of facts independent
of those relating to the Niagara gorge) is strongly confirmed by
this new line of evidence.

So far as I can see, the only question of serious doubt that can be

lo ESTIMATING THE AGE OF NIAGARA FALLS.

raised respecting this calculation will arise from the possible supposi-
tion that, when the eastern drainage over the Niagara channel be-
gan, the land stood at such a relatively lower level as would reduce
the height of the fall to about half that of the present escarpment at
that point; when it might be supposed that a protecting talus had
accumulated which would interrupt the lateral erosion for the in-
definite period when the drainage was being drawn around by way
of the recently opened Lake Mpissing and Mattawa outlet. Then,
upon the resumption of the present line of drainage, with the land
standing at nearly its present level, the talus may have been undercut,
and so fallen down to leave the upper strata exposed as at present.
But there does not seem to be sufficient warrant for such a supposition
to make it necessary seriously to entertain it, while the objections to
it are significant and serious. First, the present narrowness of the
river at the water level is such that it does not give much opportunity
for enlargement after the first formation of the gorge; secondly,
the ISTiagara limestone at the mouth of the gorge is so thin (stated by
Hall to be twenty feet thick) that it would not form a protecting talus,
even at half its present height.

P. S. — Since the above was wiitten there has been reported in
the papers an immense fall of rock from the east side of the gorge,
near the head of the Whirlpool rapids. The estimate made of the
amount is one hundred thousand tons. If that estimate is correct,
it is a very impressive illustration of how the average fall of mate-
rial from the side of the gorge is occasionally increased by a single
instance. In making our calculations above, the total amount of
material annually falling off from the portion of the side of the gorge
under consideration amounted only to 1,237 tons, while the amount
of material was 611 cubic yards. But the 100,000 tons which came
off in a single slide a few weeks ago would be equal to twenty inches
in thickness from the whole face of the cliff, where our estimate was
only a quarter of an inch.

N. B. — In the diagram (Fig. 6) extend the Niagara shale (2) up
to occupy lower two layers of (1), thus making Niagara limestone (1)
half as thick as now.

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