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4

DEPARTMENT OF THE INTERIOR—U. 8. GEOLOGICAL SURVEY
J. W. POWELL DIRECTOR

CONTRIBUTIONS

TO THE

HISTORY OF LAKE BONNEVILLE

BY

G. K. GILBERT

t
EX?TRACr FROM THE ANNUAL RePORT OF THE Dikkcror oF THR U. S. GRoLocicaL SURVEY—1880-81

 

WASHINGTON
GOVERNMENT PRINTING OFFICE
1882

 

 
 

CONTRIBUTIONS

TO THE

HISTORY OF LAKE BONNEVILLE.

BY

G. K. GILBERT.

 

 

167
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CONTRIBUTIONS TO THE HISTORY OF LAKE
BONNEVILLE.

By G. K. GILBERT.

 

I. INTRODUCTION.

In the organization of the Geological Survey by Mr. King, the teriitory
subject to its operation was apportioned in a number of divisions. To
each division a scientific corps was assigned, and in order that the labors
and results of each corps might be characterized in the highest practica-
ble degree by unity each geographic district was made to correspond to
a great geologic province. The Division of the Great Basin is a prov-
ince characterized by numerous small mountain ranges, and is thereby
distinguished from its western neighbor, the Division of the Pacific,
which contains a comparatively great mountain chain, the Sierra Nevada,
and from its eastern neighbor, the Division of the Colorailo, which
includes as its chief feature the great group of plateaus of the Colorado
Basin. At the north it is limited by the British Possessions, and at the
south by the Mexican boundary, and it has an extent nearly twice as
great as the astern and Middle States combined. Nearly the whole of
this area is studded by mountain ridges, which are approximately par-
allel and have a meridional trend. Noneof them are of great height
nor of great extent, and they are so numerous that many have no indi-
vidual names known to the whites. Between them lie valleys filled by
the alluvium that in past ages has been worn from their summits and
sides, and in a few districts these valleys grow broad and blend together
so as to constitute plains of some extent. The rainfall of the region is
scant and the streams are few and small. Two great rivers traverse it,
but their sources are beyond its limits. The Columbia, fed by the abun-
dant precipitation of the uplands rising to the eastward, crosses in a
northwest direction to the Pacific Ocean; the Colorado, rising in the
same uplands, flows southward and westward to the Gulf of California.
From the arid tract they receive a few small affluents, but except for
the avenues opened by their waters it is scarcely probable that any
streams rising within the district would find their way to the ocean.
In the interval between the drainage basins of the two rivers there is a
large district which gives rise to no outflowing streams, but returns to

the air by evaporation all the moisture received from it as rain. It is
160
170 LAKE BONNEVILLE.

this district of continental drainage to which the title “Great Basin”
ig specifically applied, and it is from it that the Division receives its
name. The geological survey of the Division involves the study of a
wide range of topics. Not only does each mountain consist of a variety
of geologic strata and embody a history of its own, but the district as a
whole contains every great known group of formations, and their study
cannot be conducted without a coincident study of the greater dynamic
problems of geologic science. The Archean, the Paleozoic, the Mesozoic,
and the Tertiary systems are each developed in so many localities that
no one of them can be studied fully without traversing a large portion
of the entire area. Volcanic rocks abound in all parts, and phenomena
pertinent to the study of the growth of mountains and the decay of
mountains are everywhere present.

With the limited means at the disposal of the Survey it was manifestly
impossible to occupy the entire field at once and carry on the work in a
way that would be both geologically and geographically symmetric.
It was necessary to restrict attention, and the question arose whether
this should be done by selecting a limited district for initial work and
beginning in it the study of every topic to which it might contribute,
or by choosing a specific line of inquiry and carrying it through the
entire area. The latter course was decided on, and the theme of
study selected was the Quaternary history of the valleys of the Great
Basin. It was already known that many of these valleys which are
now destitute or nearly destitute of water, had contained, at a period of
time geologically very late, a series of lakes, some of which were salt
and some fresh; and it had been more than surmised that these lakes
were the contemporaries of the glaciers of the Ice Epoch. The study of
their history was therefore nearly identical with the study of the Qua-
ternary history of the valleys, and it was to them that attention was
chiefly directed.

The lowlands of the Great Basin are valleys without drainage to
the ocean, and when the climate of the Glacial Epoch gave them a
more generous supply of moisture the surplus was accumulated in their
lower parts in quantities which bore a definite relation to the climate.
When for centuries the climate became more humid the lakes rose and
encroached upon the land, and when the reverse was true and aridity
prevailed they dried away and the land was laid bare. The extent of
the lakes was therefore the measure of the climate, and if we can rightly
interpret the traces the lake margins have left of their successive posi-
tions we shall be furnished with a detailed history of the oscillations
of climate in this region of the earth during that epoch. The problem of
Glacial climate is one of the most interesting which now claims the
attention of geologists, and if these Quaternary lakes can afford an in-
dependent history of the climatal changes by which the accumulations
of ice were made and dissipated, they will make a most acceptable con-
tribution to the subject. ;
GILBERT.] THE GREAT BASIN. 171

Closely interwoven with the history of the oscillations of the water is
the history of the sediments deposited by it, and the general study
cannot be carried forward without at the same time investigating the
conditions of sedimentation in inland seas. It is therefore hoped that
the progress of the investigation will add something to our means of
distinguishing, among the older geologic formations, strata which were
formed under similar conditions, and will thus enable us to read more
clearly some of the earlier pages of the geologic record which are now
obscure.

Another collateral subject of investigation is the process of shore for-
mation—the process, that is, by which the waves of a lake modify the
configuration of the land upon which they break, and produce the pecul-
iar topographic features characteristic of shores. This study has already
been successfully pursued by others on the margins of existing bodies
of water, but there are some details in the anatomy of shores which are
necessarily concealed by living bodies of water, and can only be revealed
by the dissection of the denuded remains of dead lakes.

The desiccation of the old lakes caused the concentration of their
mineral contents, so that all of them which survive with diminished
area are saline, and the positions of those which have entirely disap-
peared are marked by deposits of salt and other soluble minerals. The
study of the Quaternary lakes is therefore inseparable from the study
of the modern salines, and it may reasonably be anticipated that the
final discussion of the results will throw new light upon the saliferous
deposits of the older rocks.

At the time of the organization of the Survey it chanced that there
was in the possession of the writer a considerable body of unpub-
lished material bearing upon Lake Bonneville, and that lake was there-
fore selected as the first individual subject of study. Its investigation
in the field has now been completed, and a full account of its history,
so far as it has been found practicable to deduce it, is in preparation.
But while this history will be monographic as regards Lake Bonneville,
it will in another sense be only one of a series—to be followed in time by
similar accounts of other Quaternary lakes, and eventually by general
discussions of the various collateral topics developed by the investiga-
tion.

In the present paper it is proposed to give in brief the principal results
of the year’s work, reserving for the monograph the full presentation of
the facts from which they are derived. They will be prefaced, however,
by an outline of the subject as previously known, for the literature of
Lake Bonneville is so scattered that a general familiarity with it cannot
be assumed.

Whoever makes a careful examination of a tract of sea coast, first
before a great storm and again after the storm has passed, cannot fail
to discover various modifications wrought by the storm in the form or
character of the coast. Wherever the water margin is overlooked by
172 LAKE BONNEVILLE.

a cliff it will be found that some portion of the rock or earth of the cliff
has been washed away, and probably that fragmeuts great or small have
fallen from above. Wherever the shore is constituted by a beach or
spit it will be found that additions have somewhere been made to the
sand or shingle, and possibly that at other points losses have been sus-
tained. It is universally recognized that these changes are the result
of the conjoiaed action of waves and currents set in motion by the
storm, and that they are limited to the immediate vicinity of the shore
and to shallow water. There is a horizontal zone of activity practically
corresponding with the zone which receives the force of the breakers,
but extending somewhat farther downward, and along this zone nearly
every portion of the coast either suffers abrasion or else grows by addi-
tions to its banks and bars. Where the coast is abraded, the zone of
wave beating is carried progressively landward, and two features are
wrought: the paring away of the land leaves a fringing terrace or shelf
just beneath the water; and the same excavation produces a cliff at the
landward margin of the terrace. Where the coast grows, its banks and
bars are not merely enlarged, but if they did not before exist they are
created. The sea-cliff and the terrace at its foot are the creatures of the
wave and mark the spot where the nature of its action is destructive.
The spit, the beach, and the bar are equally the creatures of the wave,
and testify to its constructive energy.

In this way there arises a special topography of coasts, and when the
waters of a sea or lake recede or disappear, the topographic features
which were wrought by the waves survive, constituting a conspicuous
and almost unmistakable record. Every element of this record is char-
acterized by horizontality; the landward edge of the wave-cut terrace
is a horizontal line coincident with the level base of the sea-cliff; the
beach and the spit and all other constructive works are level-topped,
having been built upward to a limit regulated by the force of the
storm waves. When, therefore, one views a slope from which an an-
cient lake has been withdrawn he recognizes its shore trace in a series
of features which embody a horizontal line. Here the line is the meet-
ing of a terrace and a cliff, there it is the crest of an embankment, and
elsewhere it is the brow of a delta plain; its manifestations are diverse,
but it is never wanting. To an eye placed at the proper height and dis-
tance all its elements blend together and it stands forth as a continu-
ous, horizontal, indubitable shoreline.

It is by records of this character that Lake Bonneville is chiefly known.
All about the great basin of Utah the lower slopes of the mountains
are skirted by these level tracings—not a single line merely at a single
level, but a series of lines at many levels, testifying to a system of oscil-
lations of an ancient Jake.

The highest water line is 1,000 feet above the level of Great Salt Lake,
and over every foot of the intervening profile can be traced evidence of
the action of waves. There is, however, a great inequality of the record,
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GILBERT. } THE OUTLET. 173

and the most casual observation shows that the water lingered much
longer at some stages than at others. One of the most conspicuous
water lines is the highest of all, but its prominence is largely due to the
fact that it marks the limit between the wave-wrought surface below
and the rain-sculptured forms which rise above. Of the lower lines
there is one lying about 400 feet below the highest, which is far more
conspicuous than any other and has for this reason been given a special
name—the Provo shoreline. The highest is distinctively known as the
Bonneville shoreline. Between the Bonneville and the Provo four or
five prominent lines can usually be seen, to which no individual names
have been given, and it will be convenient to call these in this place the
Intermediate shorelines. On the slopes below the Provo shore the water
lines are less conspicuously drawn, and only a single one is so accent-
uated as to have been identified at numerous localities.

A lake without outlet cannot maintain a constant level, because its
quantity of water depends upon the relation of the rainfall to the super-
ficial evaporation, and these elements of climate are notoriously varia-
ble. A series of moist seasons increases its contents and causes its mar-
gin to advance upon the land, while a succession of dry seasons produces
the reverse effect and makes it shrink fromits borders. With alake hav-
ing a discharge the case is different, for every increase or diminution of
supply, by slightly raising or lowering the surface, increases or dimin-
ishes the discharge, and thus a practical equilibrium is maintained. It
can therefore rarely happen that the waters of a lake without outlet are
held at one level for the time necessary to produce a strongly marked,
individual shoreline, and for this reason it was early surmised that Lake
Bonneville found an escape for its surplus waters at the times of the for-
mation of the Bonneville and Provo shorelines. Search was therefore
made for a point of outlet, and eventually it was discovered at the north-
ern extremity of Cache Valley. The sill over which the water at first
discharged was of soft material which yielded easily to the wear of the
running water and permitted the lake level to be rapidly lowered by the
mere corrasion of the outflowing stream, but eventually a reef of lime-
stone was reached by which the erosion was checked and the lake was
held at a nearly constant level until its outflow was finally stopped by cli-
matic changes which diminished the water supply. The level of the soft
sill first crossed by the outflowing water is the level of the Bonneville
shoreline at the nearest point where it is visible; the level of the lime-
stone sill is coincident with that of the Provo shoreline; and the dis-
covery of these facts correlated in a satisfactory manner the history of
outflow with the history of the most conspicuous shorelines. As will
presently appear, it was the work of the past summer to complement
this knowledge by obtaining an interpretation of the Intermediate shore-
lines.

The detritus the waves bear away from one part of a coast is not all
accumulated in the adjacent embankments; only the sand and gravel
174 LAKE BONNEVILLE.

are there collected, and the finer matter, which is capable of being
held in suspension by the water for a longer time, is borne to a greater
distance from the shore and finally settles to the bottom in the form
of mud. Moreover, the streams which flow from the land to a lake
bring with them each its quota of mud too fine to subside quickly, and
this, too, is deposited in the depths remote from the shore. Thus the
whole surface of every lake bottom becomes coated with a fine mud de-
rived from the demolition of the surrounding land by rains and rivers
and by waves.

Nor is this all: the wear of the rains and even the wear of the waves
is not limited to abrasion, but includes algo solution. AJl rock material
is to some extent soluble by water, and every river carries to the sea
or lake into which it empties not merely gravel and sand and silt,
which are visible to the eye as impurities, but various minerals so inti-
mately combined that the eye cannot detect them, although they are
readily discovered by chemical tests. A lake which receives the water
of a river or rivers, and is itself drained by an outflowing river, catches
in its sediments the mechanical detritus only, which settles to the
bottom where the current is checked, and permits all or the greater
part of the chemical contents of the water to escape; but a lake with
no outlet accumulates the entire mineral contents of the tributary
streams, storing the mechanical detritus as a sediment, and the dissolved
minerals either as a precipitate or else, by the aid of animal life, in some
form of organic débris. The record of a lake is therefore written, not
only by its wave-wrought shorelines, but by its mechanical and chemi-
cal sediments, and the investigation of Lake Bonneville necessarily
included a study of the beds deposited upon its bottom. The work
of the first year of the Geological Survey demonstrated the divisibility
of these deposits into two members, separated by a break or interval
during which no deposit took place. In the work of the second year the
distribution of the two members and of the break were widely traced, so
that now it is possible to give a comprehensive description of them.

In the central and deeper portions of the basin the section of the de-
posits is as follows:

First and lowest, the Yellow Clay, a fine, argillaceous, laminated de-
posit, with a pale olive tint where unoxidized, but exhibiting on weathered
surfaces a dull yellow color. In a few spots this has been found inter-
banded with sand, but these interruptions are not continuous and its
typical exposures exhibit clay only. Its thickness is unknown, the base
of the deposit not having been seen, but 90 feet have been measured in
one locality.

Second and highest, the White Marl, a fine, white earth, exhibiting
little change from exterior to interior, and in its hardest varieties re-
sembling chalk. Its thickness varies from 10 to 20 feet.

At all points the line of demarcation between the two deposits is
strongly drawn, and at many points there has been found evidence
GILBERT.} BREAK IN SEDIMENTATION. 175

of a break in the continuity of the deposition at this horizon. This evi-
dence consists in part of traces of erosion of the surface of the Clay
before the deposition of the Marl, and in part of the local interpolation
of various coarse deposits due to superficial streams.

These relations will be made clear by the diagram, which exhibits
the lake strata in section at a point where they rest against a steep
mountain slope of quartzite. The Clay and Marl (2 and 4) are fine in
texture, and have their bedding marked by laminz, which are nearly
horizontal. In the direction to the left of the drawing they extend for
many miles without interruption. The wedge of gravel which sepa-
rates them, and the similar wedges above, are all restricted to the

a
y) ]

Fic. 17. Section showing the alternation of lacustrine and alluvial deposits at Lemington, Utah.

1. Paleozoic quartzite. 2. The Yellow Clay (lacustrine). 3. Wedge ot alluvial gravel. 4. The White
Marl (lacustrine). 5. Recent alluvial gravel. 6, Terrace and sea-cliff of the Bonneville shoreline, with
recent talus at foot of cliff.

 

 

vicinity of the mountain; they are composed of fragments of the quartz-
ite, cracked away by frost and washed down by rain. The process
of their formation still continues, and those numbered 5 and 6 receive
additions with every storm. When 2 and 4 were formed the lake bathed
the foot of the mountain, and was the vehicle for the distribution of
their fine material, but the intervening wedge of gravel, which was
washed to its place by rain and rain-born rills, could not have been
formed in the presence of the lake. It testifies, therefore, to a tem-
porary subsideuce of the water, and a drying of the bottom of the lake.

Neither the Clay nor the Marl passes beyond the limit marked by the
Bonneville shoreline, but they rise upon the slopes on all sides until they
merge with the shore deposits. As they approach the outer shore-
lines, however, they undergo changes of character and their distinctive
features disappear. Their texture becomes coarser and they pass at
many points into sands. In such case their separation can be made
only where the evidence of the intervening break is present.
176 LAKE BONNEVILLE.

Il. THE HISTORY OF THE OSCILLATIONS.

The g2neral interpretation of these deposits and of their discontinuity
is not difficult. The Yellow Clay was thrown down from deep and quiet
waters, and therefore marks a period when the lake was large. It has
been traced upwards along the slopes to within 200 feet of the highest
water mark, and it is therefore known that the body of water to which
it belonged attained at some time a depth of more than 800 feet, although
there is no reason to suppose that that depth was continuously main-
tained through the whole period of deposition. The break between the
two beds, with its local deposits of alluvium, records with equal clearness
a period when the lake shrunk to small size, laying bare the surface
of the Yellow Clay and exposing it to waste by running streams and to
partial burial by subaerial agencies. This evidence has been traced
continuously downward to a level only 200 feet higher than the surface
of Great Salt Lake, and is there lost because modern erosion has ex-
posed the section no farther. The shrunken lake could therefore have
had no greater depth than 200 feet (plus the depth of Great Salt Lake),
and its depth may have been much less. The White Marl, like the Yel-
low Clay, is a deposit from deep and quiet water, and unmistakably re-
cords a second rise of the lake. It has been traced as far up the slopes
as the Clay, and there is some evidence, as will appear farther on, that
it witnessed even a higher stage of the water during a portion of the
period of its formation. Above the Marl the only deposits are shore
embankments and recent alluvia, from which we are permitted to con-
clude that there has been no similar rise of the water since the retire-
ment of the second flood.

There can be no question of this history so far as it goes, and any
changes which may be made in it must be of the nature of additions.
The climate of the region was moist and Lake Bonneville was large
for a period represented by 90 feet and more of Yellow Clay; the cli-
mate was dry and the lake was small for an unknown period repre-
sented by the intervening alluvia; there was a second epoch of moist
climate and expanded Jake represented by 15 feet of White Marl; and
that was followed by the present period of shrunken waters and dry
climate.

But while this history is the necessary deduction from the facts in
hand it does not include all of them, for it fails to account for the con-
spicuous difference in character between the Clay and the Marl. The
character of the surrounding country affords no warrant for the belief
that there was a large difference in the nature of the detritus brought to
the lake during its two periods of maximum extent, and the explanation
of the change in the character of the deposit must therefore be sought
in the lake itself. The first hypothesis broached in regard to it was that
GILBERT. | CHANGE FROM CLAY TO MARL. 177

it was dependent upon the establishment of an outlet, but this had to
be abandoned. The establishment of an outlet would undoubtedly pro-
duce a change in the character of the water and a corresponding change
in the character of the sediment, but it could only occur during a period
when the lake was exceptionally full, whereas the change indicated by
the difference between the Yellow Clay and the White Marl occurred
at a time when the lake basin was exceptionally empty. Moreover, the
effect of an outlet upon the character of the water would be to deprive
it of a large share of its dissolved matter, and therefore to give to its
sediments a relatively pure mechanical character, whereas the sediment
which actually formed in the deeper places after the change is especially
characterized by carbonate of lime, a mineral almost necessarily brought
to the lake in solution.

For the purpose of determining, so far as practicable, the ratio of the
chemical to the mechanical elements in the sediments of the lake a series
of specimens, selected to represent the Olay and the Marl, were sub-
jected to chemical analysis. Each bed was found to consist of the same
constituents, but in different proportions, as will appear by the follow-

ing generalized table:
YELLOW WHITE
CLay. MaRL.

Perct. Per ct.

Carbonate of lime and magnesia (the lime predominant) .... --.-..-- 30 45
Silicates of alumina, iron, and other bases (alumina predominant).... 35 20
BLL R Co sicsc:siai Actsintety eg parainié: tsisrsinssreipininisislalssctelaie wejeiik'y: vswinisiars.e wiaibia'sin Warstevele 35 35

The carbonates possess so high a degree of solubility that they may
be referred to the rank of chemical deposits without hesitation. The
silicates have so low a degree of solubility that they may be referred
with equal confidence to the rank of mechanical sediments. The silica
holds an intermediate position and may be either mechanical or chemi-
cal, or may belong in considerable share to each division. However the
silica is assigned, there is no reason to doubt that it has the same
origin in both deposits, so that in any event the Marl contains a rela-
tively large proportion of matter derived by chemical precipitation
and the Clay a relatively large proportion of material conveyed by the
water in suspension.

With these facts in view a second hypothesis was broached to ac-
count for the lithologic difference. Itis shown by the stratigraphy that
in the interval between the deposition of the clays and the marls the
water fell below the 200 feet contour, but the stratigraphy fails to
show how far below that line it fell. There is no violence in the suppo-
sition that the water dried completely away so that no lake whatever
remained, and that all of the salt that may have been contained in the
original lake was deposited by desiccation upon the lowest part of the
lake bottom. Nor is there any violence in the further supposition that
during the dry period the silt brought down by rivers in time of freshet
was spread over the bottom of the lake valley, mingling with the salt

WGA
178 LAKE BONNEVILLE.

at first and then covering it, until finally it was buried so deeply that
the rising water, when the lake was again filled, did not redissolve it.
By such a process the lake would be converted by desiccation from a
salt body of water to a fresh body, and whatever influence loss of
salinity might have upon the conditions of sedimentation would be
indicated by an abrupt change in the character of the deposits.

Tor the verification of this hypothesis it is necessary to ascertain that
the change which actually occurred in the nature of the sediment is
such a change as would be produced by substituting fresh water for brine
as the medium of sedimentation, and for its complete verification it
would be necessary to probe the deposits in the lowest depression be-
neath Great Salt Lake and ascertain the existence of a heavy bed of
rock salt. It was impracticable to undertake the latter investigation,.
but a series of experiments were conducted for me by Mr. Israel C. Rus-
sell, for the purpose of ascertaining what relation salinity of water bears
to facility of sedimentation. No attempt was made to give a general
character to the investigation, but it was made specifically applicable
to the problem in hand by selecting for its materials the substances actu-
ally In question. The water of Great Salt Lake, which contains about
15 per cent of saline matter, was made to represent the supposed ancient
brine of Lake Bonneville. The water of City Creek, a stream flowing
through a calcareous district in the Wasatch Mountains and one of the
tributaries of the Bonneville Basin, was taken fo represent the water
of Lake Bonneville in its supposed fresh condition, and specimens of
the clay forming the lower bed of the lacustrine series were taken to
represent the mechanical clement of the Bonneville sediments. A
chemist’s beaker was filled with the brine, another with the creck water,
and a series of others with various definite mixtures of brine and creek
water. The clay was pulverized and divided into equal portions, which
were severally added to the different beakers and mingled by stirring.
Observation was then made of the time required by the different mix-
tures to become clear. The experiment was subsequently varied by pre-
paring first those mixtures of which the clearing was found to be slow-
est, and then after an interval other mixtures observed to clear more
rapidly, and then noting after what lapse of time they attained the same
degree of approximation to clearness. It is unnecessary to give here
the detailed results, but it is sufficient to say that they all point in the
same direction and show that the clay falls much more rapidly from
City Creek water than it does from the Salt Lake brine, while its rate of
falling from various intermixtures is proportioned to the percentage of
brine. The degree of clearness attained with the City Creek water in
twenty-four hours was reached with the Salt Lake brine only after a
lapse of five days.

Evidently, then, if Lake Bonneville possessed the salinity of Great Salt
Lake its mechanical sediment would be much longer retained by the water
and would therefore be more evenly distributed than if it was charac-
GILBERT. ] EXPLAINED BY DESICCATION. 179

terized by the freshness of City Creek; and since the mechanical sedi-
ment necessarily entered the lake at its margin, being derived from the
tribute of muddy streams and from the waste of the coast under the
action of waves, it would in a fresh lake be largely deposited in the
neighborhood of the shore, while in a salt Jake it would be transported
to greater distances before reaching a final resting place, and although
possibly the upper slopes would still receive the lion’s share a consider-
able portion would nevertheless find its way to the central region. The
hypothesis of a loss of salinity during the interval between the deposi-
tion of the Yellow Clay and the White Marl accords therefore with the
observed difference between those deposits. The upper and later-formed
deposit, which hypothetically marks the prevalence of fresh water, is
characterized by a smaller proportion of mechanical sediment, and its
calcareous constituents, which thus acquire relative importance, are
rendered conspicuous.

It is a necessary part of the hypothesis that the contrast of sedi-
ment exhibited by the Marl and Clay in the central area is reversed
at the margins of the basin; for if it is true that the material fur-
nished to the lake had always the same character, and that the contrast
of the upper and lower deposits of the central area depends on con-
ditions of distribution, then the small clay content of the White Marl
at the center should be complemented by a large clay content of the
shoreward prolongations of the same deposit; and in peripheral regions
the lower bed should be more calcareous than the upper. As a matter
of observation this has not been shown, but at the same time it has not
been disproved. Both Marland Clay become so variable and so coarse in
the vicinity of the shores that a concise diagnosis of their constituents is
impracticable. Whatever calcareous matter they contain is so masked
by silicious and argillaceous material that it does not affect them in a
manner appreciable to the eye, and chemical determination could not be
brought to bear by reason of their variability, which made it impossible
to select representative specimens.

It is possible that the contrasted conditions afforded by brine and
fresh water may conduce to the observed disparity of sediments in yet
another way. It is a familiar fact of the laboratory that the mingling
of concentrated solutions of common: salt and of carbonate of lime
induces a precipitation of carbonate of lime, and although such a result
is not observed when the waters of City Creek and Great Salt Lake are
mingled, it may nevertheless be possible that a reaction of that nature took
place about the margins of Lake Bonneville in its supposed briny phase.
If it occurred, then the chief part of the chemical sediment would be
accumulated near the shores, while a relatively small share would reach
the central region. Afterward, when the water was freshened, the pre-
cipitate would in the absence of this reaction be equable in all parts,
and a relatively greater proportion of carbonate of lime would be thrown
down in the central region. It is noteworthy, however, that the off-
180 LAKE BONNEVILLE.

shore equivalents of the Yellow Clay afford to superficial observation no
indication of the presence of an exceptional] share of precipitated car-
bonate of lime; so that while this consideration might help to sustain
the general hypothesis it is not definitely sustained by facts of obser-
vation.

On the whole, the theory that the lake became fresh by desiccation
finds too little positive support to entitle it to unreserved acceptance,
but is controverted by no single known fact, and may therefore be con-
sidered to hold the position of a plausible working hypothesis. A series
of investigations which have already been initiated by Mr. Russell in
regard to the deposits of numerous natural evaporation pans of the
Great Basin must eventually enable us to form a better judgment in
regard to it than is possible at present. If it shall be established, a
valuable addition will be made to the history of the ancient lake, for it
will be shown that the climate in the inter-Bonneville epoch was so much
drier than the climate of the present day that the water surface of tbe
basin, which now has an extent equal to one tenth that of the broadest
area of Lake Bonneville, completely disappeared. In our tentative his-
tory of the lake and the climate, subject always to revision with the
addition of new facts, we cannot do better than to incorporate this ele-
ment.

We now turn from the history written by the sediments to the con-
temporaneous history written by the shorelines.

Before the existence of Lake Bonneville its basin was dry, or nearly
so. The water rose at the beginning of the epoch represented by the
Yellow Clay, and receded to the base of the slope at the close of that
epoch. It rose and feil again at the beginning and end of the epoch
represented by the White Marl. Thus its margin was carried four times
over the slopes of the basin, and every part of the profile was four
times subjected to the action of the waves. In localities so circum.
stanced that the work of the waves was destructive, a portion of the land
being eaten away, each successive attack cut deeper into the rock or
earth and obliterated the traces of preceding attacks. In localities so
circumstanced that the work performed by the waves was constructive,
embankments of detritus being added to the pre-existent surface, each
successive advance or recession built its embankments upon those which
had previously been made and wholly or partially concealed them. The
series of shorelines last formed are, therefore, generally speaking, the
only ones visible, and the actual configuration of the surface is, in gen-
eral, that wrought by the last passage across it of the water margin.
Since the water is now at low stage, the last passage was a recession,
and it was therefore assumed, both by the writer and by others, during the
earlier progress of the study of the lake, that all of the visible shorelines
represent lingerings of the water during its last recession. When, how-
ever, it became known that the portion of that recession included be-
tween the Bonneville and Provo shorelines was caused by the gradual
GILDERT.] OVERLAP. 18]

cutting away of the barrier at the point of outlet, a difficulty arose, for
the interval between the Bonneville and Provo shows in many places a
number of well-characterized (Intermediate) shorelines, and it appeared
strange that the rate of lowering should have been so irregular as to
have permitted their formation. It was at first suspected that the linger-
ings of the water might have been determined by ledges of exceptional
hardness in the material through which the outflowing channel had to
wear its way, but an examination of the point of outlet gave no indica-
tion of the existence of such ledges. The idea then suggested itself
that the phenomena were due to oscillations of climate, whereby the
volume of discharge had been alternately increased and diminished, so
that the rate of erosion had been alternately rapid and very slow; and
with a view to testing this theory an elaborate study of the groups
of embankments associated with the Intermediate shorelines was un.
dertaken. The result of the investigation was entirely unexpected, but
was none the less satisfactory, for it included a determination of the
order of succession of nearly the entire series of shore marks.

When two embankments formed at successive water stages are so
far separated upon a pre-existent slope that they are entirely distinct,
they afford no means of determining their relative age, but if they are
contiguous, one must always overlap the other in some way, and the de-
termination of this overlapping serves to establish the order of priority.
Thus, if the line a b of the diagram is the profile of a pre-existent
slope upon which the series of shore embankments 1, 2, 3, and 4 have
been built, then it is impracticable to determine the relative age of 2
and 3 or of 2 and 4, but it is evident that 1, which rests upon 2, must
have been later formed, and that 3 was built before 4 which rests
against it. This relation is not expressed by the external forms, for the
profile of the group 1-2, is identical with that of the group 3-4, but
purely by the manner in which they are superposed. To make the de-

 

 

Fic. 18.—Diagram illustrating the superposition of shore embankments.

termination it is necessary to have a cross-section, and in the embank-
ments of the Bonneville Basin cross-sections are rarely exposed, for
the reason that the recency of their formation has given subsequent
erosive action little opportunity to perform its work. Nevertheless,
182 LAKE BONNEVILLE.

a few localities were by patient search discovered, and although none
of them sufficed to tell the entire story it was found possible so to
combine their elements as to develop a tolerably complete history of
the series of events by which the Intermediate shorelines were pro-
duced.

A graphic transcript of that history is given in Figure 19, where
the chronologic order of the deposits is, first Y, then I, J, K, L, M, B,
and P. The series of embankments YY was not discovered in section
and the succession of its parts is unknown. I, J, K, L, and M, are the
embankments of the Intermediate shorelines and their order of forma-
tion was from below upward; that is to say, they were built by the
rising water and not by the faliing. B is the Bonneville shoreline,
formed after the completion of the Intermediate; and P, the Provo, last
of all. The series YY records the first rise of the water and is the lit-
toral equivalent of the Yellow Clay. It shows that the water at that
time reached an extreme level about ninety feet lower than the Bonneville
shore, and by so much failed to attain the height necessary to produce
an overflow. The overlying banks from B to P record the second rise
of the water and are the littoral equivalents of the White Marl. Their
order of succession shows that the water rose by gradual stages until it
reached its maximum at the Bonneville shore, and then, when an over-
flow had once been established, cut away the barrier and fell to the

 

 

 

Fic. 19.—Diagram, showing the Overlap and Chronologic Order of the Shore Embankments of the
Bonneville Basin.

Provo level with a rapidity that afforded no opportunity for a record of
the stages of its progress. At the Provo level the water was long
retained by the resistance of the limestone sill at the point of outlet,
and embankments of exceptional magnitude were formed on its shores.

It is especially interesting to learn that the second rise was higher
than the first, for this fact carries with it the conclusion that the second
great wave of climate was more strongly characterized by moisture than
GILBERT. } MOUNTAINS CARVED BY RAIN. 183

the first. Combining this information with that afforded by the sedi-
ments, we have the two climatic maxima distinctively marked: the first
was long and relatively mild; the second was short and relatively in-
tense.

It remains to consider the beginning of the Bonneville history. The
history of the lake is written by wave-sculptured topography and by
lacustrine deposits. The history of the basin before the lake is written
by rain-sculptured topography and alluvial deposits.

We are unaccustomed to think of the ordinary forms of land as a
work of sculpture, but that is none the less their origin. If we except
those restricted areas which have received their configuration from the
recent occupation of lakes and oceans and those other restricted areas
which owe their shapes to the passage of glaciers and the heapivg
of glacial débris, the whole surface of the land exemplifies the plastic
art of the rain. The work of the wind is accessory to it; subterranean
forces of upheaval and of volcanic energy give rise to mountain masses,
and variations of hardness in the rocky strata of the earth assist in deter-
minving the positions of hilis and crests and ridges; but raiu is the agent
which actually develops the forms we see. It penetrates rocks and
dissolves them; swollen by frost it disintegrates them; it beats upon
them and washes away the fragments, and gathering in rills, creeks and
rivers it erodes channels and carries the débris to the valleys and the
ocean. Its work is in the highest degree systematic, persistent and com-
plete, and it either has molded or is molding every geographic form of
nature to exemplify the laws of its action. Our eyes are so accustomed
to these forms that we unconsciously anticipate them and readily detect
the exceptional nature of all differing elements of sculpture. The sculpt-
ure wrought by the waves affords so marked a contrast that the eye
distinguishes it at once, and it is thus that the tracing of the Quaternary
lakes is made possible.

The sculpture of a mountain by rain is atwofold process; on the one
hand destructive, on the other constructive. The upper parts are eaten
away in gorges and amphitheaters until the intervening remnants
are reduced to sharp-edged spurs and crests, and all the detritus thus
produced is swept outward and downward by the flowing waters and
deposited beyond the mouths of the mountain gorges. A large share
of it remains at the foot of the mountain mass, being built into a smooth
sloping pediment. If the outward flow of the water were equal in all
directions this pediment would be uniform upon all sides, but there is a
principle of concentration involved whereby rill joins with rill, creek with
creek and gorge with gorge, so that when the water leaves the margin
of the rocky mass it is always united into a comparatively small number
of streams, and it is by these that the entire volume of detritus is
discharged. About the mouth of each gorge a symmetric heap of allu-
vium is produced—a conical mass of low slope, descending equally in all
directions from the point of issue; and the base of each mountain ex-
184 LAKE BONNEVILLE.

hibits a series of such alluvial cones, each with its apex at the mouth of
a gorge and with its broad base resting upon the adjacent plain or valley.
Rarely these cones stand so far apart as to be completely individual
aud distinct, but usually the parent gorges are so thickly set along the
mountain frout that the cones are more or less united and give to the
contours of the mountain base a scalloped outline.

The Bonneville Basin is surrounded by and interspersed with mount-
ains, and from the summits of these down to the Bonneville shore the
entire topography is of a rain-wrought type. T'rom the sboreline down-
ward to the valleys and plains its nature is composite, uniting the ele-
ments of wave sculpture with those of rain sculpture, but the manner
of union is not indiscriminate and in it is written what we know of the
pre-Bonneville history of the basin. Allof the larger elements belong
to the domain of rain, and upon these the elements derived from wave-
work are lightly engraved and embossed. The alluvial cones of the
mountains do not find their bases at the level of the upper shoreline, but
extend downward uninterruptedly to the bottoms of the valleys, while
the shorelines are wrapped about them, all of the greater capes and bays
being determined by a pre-existent, rain-wrought configuration. Rain
therefore dominated the basin before the lake, and the basin was empty
for a long period before it was full.

The same story is told by the deposits. The alluvial cones are sub-
aerial deposits, the lake beds subaqueous; and wherever a section of the
latter is obtained upon the margins of the basin they are found to overlie
unsorted accumulations of alluvium. The two are so distinct in charac-
ter that they cannot be confused. The lake beds are fine earths, evenly
laminated, and of great uniformity throughout the central district.
Toward the margins they usually become coarser, passing into sands at
first and being finally exchanged at the shore for thoroughly sorted
gravel, smoothed and rounded by the rolling action of the waves. In
the alluvial deposits no stratum is widely continuous and few are homo-
geneous, but coarse and fine fragments are mingled indiscriminately or
with an obscure and lenticular bedding.

Form and substance thus conspire to prove that the lake had a be-
ginning as well as an end, and that before its inception the basin was
for a long time subjected to the ordinary laws of sculpture by the
action of rain. It must not be supposed, however, that the period of
exclusive rain sculpture was one of great aqueous precipitation, but
rather the contrary. A large rainfall would fill the basin and subject
its lower parts to lacustrine influence. Only a small precipitation, or a
climate of relative aridity, could leave the lower valleys dry and give
the entire slope to the unrestricted action of such rain as fell. The evi-
dence of ancient rain sculpture in the lower slopes is therefore in this
case the evidence of an arid climate instead of a humid one, and our
data warrant the belief that the Bonneville epoch was an episode of
moisture interpolated between the aridity of the present day aud the
aridity of the past.
‘SSHNOD TVIANTIV

 

 

T88I LUOdFY TVANNY “AYAYIS TFITOOTOZ 9S 2

HIAX NN CTd
acne BURIED MOUNTAINS. 185

It is probable that with the diminished rainfall of the present day
the wear of the mountains is slower than during the Bonneville epoch,
and it is probable that it was similarly slow during the ante-Bonneville
period of aridity. Detritus was therefore furnished less rapidly for the
construction of the old alluvial cones than for the building of lake strata,
and the magnitude of the cones as compared with the lake beds would
lead us to ascribe an immensely greater duration to the ancient dry cli-
mate than to the epoch of moisture. It is to be borne in mind, however,
that a moist period could make its record by shorelines and lake beds
only on the condition of the existence of a closed basin, and it is a matter
of geologic history that the Bonneville Basin came into being after the
deposition of the latest Tertiary deposits known in the region. It is im-
possible to tell what fraction of the work of the construction of the allu-
vial cones was performed after the occurrence of the upheavals and sub-
sidences to which the basin owes its origin, and it is therefore impossi
ble to assign even a proximate limit to the duration of the dry epoch
demonstrated to have preceded the Bonneville humidity; but it may
be asserted with confidence, that the duration of the earlier period
was not merely greater than that of the Bonneville but many times
greater, for the condition of the various passes which constitute the
lower parts of the rim of the basin suffices to show that the waters were
not discharged for a very long period antecedent to the Bonneville out-
flow.

It follows from what we have said of the sculpture of mountains that
an. alluvial foot-slope is a necessary concomitant of an angular summit.
It is impossible that the higher parts should be carved into peaks and
scored into gorges without the accumulation of eroded material at the
foot of the slope. But in the central parts of the Bonneville Basin, in
the midst of the Great Salt Lake Desert, there are mountain peaks
springing abruptly from the lake sediment without visible pediments of
alluvium. They jut from the plain as abruptly as islands jut from the
ocean, and the resemblance is so striking that it has caught the eye of
the frontiersman and prospector, and the peaks have received such names
as “Silver Islet,” “Desert Island,” and “Newfoundland.” The resem-
blance involves something more than mere analogy, for they are really
submerged, having their bases buried by the lacustrine deposits of Bon-
neville and earlier lakes. They serve to carry us back one step farther
in the history of the basin, for they record a time when the visible
lacustrine strata did not exist and when the relation of altitudes was
such that the detritus from the peaks, instead of being arrested where it
now is by the plain, was free to descend the slope for an additional dis-
tance of at least some hundreds of feet. At that time the basin may
not have been a basin and may have permitted its drainage to escape
to the ocean; but during the whole period required for the burial of
the mountain bases its barriers must have been in existence so as to
render the desert the repository of detritus. Before Bonneville Lake,
186 LAKE BONNEVILLE.

é

therefore, there was a long history of smaller lakes in the Bonneville
Basin. This history we cannot read in detail because the sediments
which record it lie beneath the plain, completely buried by those of the
later lake.

Putting together all these several elements we may construct the
Bonneville history with some confidence:

1. A long period of dry climate and low water, during which the
mountains of the desert were buried and the alluvial slopes of marginal
mountains were formed.

4. A period of moist climate and high water, during which the Yellow
Clay was deposited and the shore was carried within ninety feet of the
summit of the lowest barrier of the basin.

3. A period of extreme dryness, during which the lake disappeared
and its salt was buried.

4, A relatively short moist period, during which the White Marl was
thrown down and within which the water overran the barrier, diminish-
ing by erosion its height at the point of discharge.

5. The present period of relative dryness.

 

 

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J

Fic, 20.—Curve of the Quaternary Oscillations of Climate, as recorded by Lake Bonneville.

In the diagram an attempt has been made to give a graphic repre-
sentation of these oscillations of climate. The lower horizontal line
represents the dry climate of the present day. The upper horizontal
line represents a climate with such a degree of moisture as to permit
the basin to overrun its rim. The relative proportions of the curve are,
of course, tentative and crude, for the investigations have afforded no ab-
solute time gauge and very little that can be interpreted in time ratios.
We know that the moisture was greater at the time of the second rise
than at the time of the first, but have no means of telling Low much
greater. We know that the earlier rise was of longer duration than the
later, but do not know how much longer, because the Yellow Clay which
represents it has never been seen in complete section. It is theoretically
probable that the inter-Bonneville dry epoch was characterized by a cli-
mate more arid than the one we experience, but we cannot say how
much its aridity exceeded the present, aud of its duration we only know
 

U.S. GEOLOGICAL SURVEY. ANNUAL REFORT 1881.

PL. N&XNIX.

 

a=

EP IFO

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aon bri cho las

VIEW ON GREAT SALT LAKE DESERT, SHOWING MOUNTAINS HALF BURIED BY LAKE SEDIMENTS.

 

 
GILBERT. } BREVITY OF QUATERNARY TIME. 187

that it was far briefer than that of the dry period preceding the first
rise of the water.

If it were possible to replace this tentative curve by the actual curve
of climatic oscillation for the same period, we should undoubtedly
have a form less simple in its character. Indeed, there is abundant
evidence that each great rise and fall recorded by the shorelines of
Lake Bonneville was interrupted by intervals of reverse motion, the
rising water occasionally hesitating and sinking for a time, and the fall-
ing water occasionally oscillating upward. It may be asserted with
some confidence, however, that the history includes but two great
waves. If the water had many times, instead of twice only, risen to
the upper levels of its range, the tell-tale sediments could not have
failed to record the intervening subsidences.

The student of the climate of the Glacial Epoch will be interested to
compare this history with that deduced from the glacial beds of Europe
and the United States, and if he correlates the second humid wave with
the Reindeer Epoch of English geologists he will be surprised to find that
in Utah the climate was more severe than during the first maximum,
although maintained for a shorter period. It is yet too early, however,
for final conclusions, for the Bonneville history is but one of a group,
and when Lake Labontan and the other lakes of the ancient family
have received a similar treatment the conjoint verdict of the whole may
be notably different from the single verdict of an individual lake.
There is a partial blank in this history, regarded as a history of climate,
embracing the period while the lake overflowed, for then its water level
ceased for a time to be an index to the amount of precipitation. There
is another partial blank during the inter-Bonneville desiccation. It is
by no means improbable that these will be filled by the evidence to be
gleaned in other valleys of the Great Basin.

Before leaving the subject of the chronology of the lake, I cannot
forbear to add my testimony to that which other geologists have ren-
dered of the extreme brevity of the Quaternary as compared with other
divisions of geologic time. If it could be measured in years its extent
might excite our wonder, but when gauged by those imperfect standards
to which geologists are limited it appears of extreme insignificance
because overshadowed by the greater magnitude of all other elements
of geologic duration. The weight of the bowlder which we strive to lift
may seem great because our strength is small, but it is a mere trifle as
contrasted with the distant hill, and we have no terms by which to com-
pare it with the mountain beyond. Such differences the geologist must
confess his inability to measure, but he is none the less impressed with
their magnitude.

If we attempt to compare the duration of the Bonneville epoch with
that of earlier portions of geologic time, we find no criteria available
except those afforded by tle relative thickness of the accumulated
188 LAKE BONNEVILLE.

deposits, and these are practically valueless because rates of deposition
are entirely controlled by extraneous conditions of which we have no
knowledge in the case of the older deposits. A better, but yet a very
inadequate, idea may occasionally be gleaned of the relative antiquity
of different events by comparing the subsequent erosion. Rain, the
great sculptor of natural forms, attacks all exposed surfaces of Jand, and
whatever may have been their original shapes, works them over until
they accord to certain types embodying a certain system of laws. Its
attacks are renewed with unwearied persistency until its ends are accom:
plished. The sediments of a dead lake are measurably protected from
it because they occupy depressions and have few slopes steep enough
to be worn by running water, but shorelines are fully exposed and are
powerless to resist. Nevertheless, the Bonneville shores are almost
unmodified. Intersecting streams it is true have scored them and inter-
rupted their continuity for brief spaces, but the beating of the rain has
hardly left a trace. The sea cliffs still stand as they first stood, except
that frost has wrought upon their faces so as to crumble away a por-
tion and make a low talus at the base. The embankments and beaches
and bars are almost as perfect as though the lake had left them yester-
day, and many of them rival in the symmetry and perfection of their
contours the most elaborate work of the engineer. There are places
where bowlders of quartzite or other enduring rock still retain the
smooth, glistening surfaces which the waves scoured upon them by dash-
ing against them the sands of the beach.

When this preservation is compared with that of the lowest Tertiary
rocks of the region—the Pliocene beds to which King has given the
name “‘ Humboldt”—the difference is most impressive. The Pliocene
shorelines have disappeared. The deposits are so indurated as to serve
for building-stone. They have been upturned in many places by the
uplifting of mountains; elsewhere they have been divided by faults, and
fragments dissevered from their continuations in the valley have been
carried high up on mountain flanks, where erosion has carved them in
typical mountain forms.

If we look back to the lower Tertiary of the adjacent plateau region
of Utah, Colorado, and Arizona, we find a still greater contrast, for the
Eocene of the Colorado Basin has not merely lost its shorelines and been
upturned and faulted; its whole great sheet, with the exception of a
few marginal fragments, has been excavated and carried away, and
with it have disappeared several thousands of feet of the strata that
lay beneath it.

The date of the Bonneville flood is the geologic yesterday, and calling
it yesterday we may without exaggeration refer the Pliocene of Utah to
the last decade; the Eocene of the Colorado Basin to the last century—
and relegate the laying of the Potsdam sandstone to prehistoric time.
OTLBERT.] THE MORAINES OF LITTLE COTTONWOOD. 189

iI. THE LAKE AND THE GLACIERS.

All geologists who have studied the Quaternary lakes of the Great
Basin and at least one student of a Quaternary lake of the Old World,
have agreed in regarding them as the contemporaries of the Quaternary
ice-fields, but their conclusions have been reached purely by analogy.
The moraines and other traces left by the ancient ice-fields are so fresh
in their appearance, so little impaired by the waste of time, that they
are regarded as the record of an epoch immediately preceding the pres-
ent time. The same is true of -the shorelines and deposits of the an-
cient lakes. It is further known that the Epoch of Ice was preceded by
a still longer epoch not so characterized, just as the Bonneville Epoch
was preceded by a longer epoch of relative dryness. More than this,
the changes of climate were analogous in character. It is a matter of
dispute whether the Glacial climate differed from that which preceded
and followed it by an excess of inoisture, or by a lowering of tempera-
ture, or by both. But whatever was its character it must have been one
in which the ratio of precipitation to evaporation was relatively great;
and that is the sole condition necessary to the production of the Quater-
nary lakes. But while this analogy is cogent and the conclusion to
which it leads finds no opponent, it would, nevertheless, be more satis-
factory to establish the relation by direct observation, and it was there-
fore with great interest that attention was turned during the field work
to a locality at the western base of the Wasatch Range where the mo-
raines of three ancient glaciers stretch below the limit of the ancient lake.
It was anticipated that if the glaciers attained their maximum develop-
ment after the culmination of the lake their moraines would be found
either to consist partly of plowed-up lake beds or else to rest upon lake
beds; and if the history of the lake was subsequent to that of the glaciers,
it was anticipated that the moraines would be found partially buried by
the lake sediments or else scored by the shorelines. Neither of these
anticipations was realized. Two of the terminal moraines were found
to be entirely dissociated from the lake beds, so far as could be ascer-
tained, and they bear no trace of wave sculpture. The remaining term-
inal, that of Little Cottonwood Cafion, is partially buried by a sandy
deposit that bears some resemblance to a river delta, but which has
been so deformed by a system of faults by which the region has re-
cently been shattered that its true character cannot be asserted with
confidence. The locality failed therefore to yield the crucial evidence
for which search was made, and practically afforded no contribution to
the subject. There is reason to hope, however, that a series of localities
announced by Mr. Russell as recently discovered upon the eastern flank
of the Sierra Nevada will prove more communicative. His reconnais-
sance has served to show that the glaciers there descended and retreated
more than once, and that their history has a determinable relation to
that of the Quaternary predecessor of Mono Lake.
190 LAKE BONNEVILLE.

IV. THE LAKE AND VOLCANIC ERUPTION.

The discovery of Richthofen that the various lavas erupted in Western
North America had a definite, uniform order of sequence has been abun-
dantly verified by all later investigations. And not only do his suc-
cessors in that field of inquiry find the order of sequence in every place
the same, but some of them at least are disposed to assign a definite
geologic date to the appearance of each variety of eruptive rock. The
cycle of eruptions to which his conclusion applies belongs to the Tertiary
and Quaternary history of the region, and the latest in order of the
erupted rocks is basalt. Basalt is therefore the only volcanic rock the
western geologist would expect to find associated with the phenomena
of the Quaternary lakes, and so far as Lake Bonneville is concerned it
certainly is the only rock thus associated. ‘The only other eruptive rock
known to appear within the circle of the shorelines is rhyolite, and all
of its masses are so ancient that they have lost by erosion all traces of
their original forms. The same may be said of some basaltic masses,
but the greater number still preserve their original tabular shapes, and
a few are still furnished with craters of cinder and slag. The majority
evidently antedate the epoch of the Jake, for they bear upon their sides
the sculptured shore marks, and support on their flanks or backs the
lake-spread sediments. To this rule, however, there are a few excep-
tions, and these serve to bring down the period of basaltic eruption to
a date subsequent to the last rising of the water.

In the vicinity of the town of Fillmore the Sevier Desert is diversified
by a group of hills composed of volcanic ejecta, recording the latest
plutonic activity within the Bonneville Basin. The extravasated ma-
terial appears in three forms, viz., coulées of lava, cratered cones of slag
and cinder, and cratered cones of tuff.

The coulées are of the usual type, but by reason of the flatness of the
surface upon which they flowed they are broadly spread, so as to con-
stitute fields rather than streams of lava. In the interior they are of
compact basalt, but superficially they are for the most part greatly in-
flated by bubbles.

The cratered cones mark in every case the points of issue of coulées
and are themselves the product of explosive action. They are com-
posed entirely of fragments which were hurled into the air from the
vent and fell about the sides, piling up circular barriers, and they are
of two distinct kinds, characterized by two kinds of fragments, slag
and tuff.

In the case of the slag cones there is every evidence that a large share
of the ejected material was either molten or pasty at the time it reached
the earth, the successive pellets being flattened out by the force of the
impact and fitted to the surfaces upon which they alighted. The in-
‘ONVOIOA ANINVWENS V “ALLAG LNVAVd

 

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oILBERT.] PAVANT BUTTE. 191

teriors of the craters are stuccoed with clots of spongy lava, which
adhered in so soft a condition as to flow and drip more or less after they
became attached. Besides these pasty masses there is a great quantity
of light, brittle, spongy material, such as has been called “cinders”
and “lapilli,” and it is possible that this constitutes the greater bulk,
but the surfaces are largely composed of taffy-like slag.

In the tuff masses, on the other hand, there is nothing to show that any
of the ejected material was soft at the time it reached its resting place.
Lapilli or cinders, similar to those which enter into the composition of
the slag cones, but finer grained, make up nearly the entire mass, and
are cemented together in a coherent body which betrays an obscure
bedding and has everywhere a brecciated appearance; in it are embed-
ded at rare intervals both rounded and angular fragments of basalt,
and these, although they have evidently reached their position by vio-
lent ejection, are not of a scoriaceous or frothy texture, but are compact.
These cones appear to have been formed by subaqueous eruption, and
are free from slug because the presence of water inade it impossible for
small tragments to escape from the vent in a hot condition.

The most conspicuous of the cones is Pavant Butte, otherwise known
as the Sugar Loaf, which stands solitary on the plain, midway between
the towns of Fillmore and Deseret. It is composed exclusively of tuff
and does not form a complete ring, but has a semi-lunar base, and ap-
pears never to have been closed upon the south side. Midway between
its base and its summit it is encircled by a terrace, carved by the waves
at the highest stage of the lake, and there is evidence that the two
processes of wave sculpture and volcanic construction were carried for-
ward, in part, simultaneously, a first incision by the waves having been
filled by new ejecta, and then partially reopened by later wave action.
Pavant Butte, therefore, is the product of eruptions which occurred
while the desert was covered by the lake, and the last addition to it was
made during the highest stage of the lake.

At its base, and apparently constituting its foundation, there is a lava-
bed half concealed by lacustrine sediments, but these sediments consist
only of the White Marls, and nowhere exhibit the underlying Yellow
Clay. It is probable, therefore, that the coulée outflowed during the
inter-Bonneville epoch of low water.

A second crater, to which the name Tabernacle has been attached,
is surrounded by two riins, the outer and older of which consists of tuff
and the inner and newer of slag. No shorelines are carved on either
tuff or slag, and no lake beds rest upon them. The eruption began,
therefore, during a high stage of the lake and was continued or re-
newed after the water had fallen below the level of the vent. There is
reason to believe, however, that the lake had not entirely disappeared,
for a lava field which outflowed from the same vent during the forma-
tion of the slag cone, bears upon its outer margin the traces of the Provo
shoreline. There is evidence also, in the exceptional thickening of the
192 LAKE BONNEVILLE.

lava bed at its outer edge, that it encountered as it flowed the refriger-
ating influence of standing water, and it is therefore concluded that
the date of the last eruption from this vent was during the Provo stage
of the lake or just before the final subsidence of the water.

A third group of craters, known as the Ice Spring group, is still more
recent, and with its associated coulées overlies the latest of the lake beds,
while no shorelines whatever impinge upon it.

The period of volcanic activity therefore continued entirely through
the epoch of the lake, and was brought down so nearly to the present
time that there is no warrant for assuming that its end has yet been
reached. No one who has seen the fresh, black, unworn surfaces of the
most recent coulées, still absolutely barren of vegetation, could be af:
fected by surprise if it should some day be announced that the now
quiescent fires had again broken forth.

Vv. THE LAKE AND MOUNTAIN BUILDING.

It isnot many centuries since the learned and ignorant alike regarded
mountains as the embodiment of stability and permanence; but since
the birth of geology it has been abundantly shown, first, that the sites
of many individual mountains were in the remote past occupied by
plains or oceans; second, that in the remote past there were mount-
ains where now are only plains; and, third, that on account of the un-
ceasing erosive work of the elements no mountain can be permanent.
Each mountain therefore has a history,—involving its inception, its
growth, its decay, and finally its extinction. With slight exception all
mountain growth is by subterranean action, and if we exclude volcanic
mountains from consideration we may refer mountain building almost
wholly to upheaval. With slight exception the destruction of mount-
ains is by erosion, and in most mountains the formative and destruct-
ive processes at some time coexist. So soon as the formation of 4
mountain is initiated, slopes are created which enable rain and streams
to wear away its surface, and since this wear never ceases until its final
and complete destruction, it is contemporary with every stage of growth
except the initiative. The magnitude of each mountain at any time
represents the excess of formation over destruction, of upheaval over
erosion. Actual increase takes place only when the growth exceeds the
decay, and actual decrease only when the decay by erosion is more rapid
than the growth by upheaval.

Up to this point all geologists are agreed; but there is a difference of
opinion in regard to the rate of formative action, and upon this differ-
ence investigators may be regarded as divided into two classes, each of
which represents a tendency of thought. On the one hand are those who
conceive that each mountain rose more or less abruptly, either by a sin-
¥

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oiLpErt.) RATE OF MOUNTAIN GROWTH. 193

gle movement at a definite point of time, or else by a small number of
such movements separated by long intervals of time. On the other hand
are those who think the formative movement is continuous and slow,
variable indeed in its rate, but never in any large way paroxysmal.
Undoubtedly there are still others who hold to a middle ground of opin-
ion, but in a general way geologists tend to catastrophism on the one
hand or to uniformitarianism on the other.

Neither of these views is open to the charge of being purely specula-
tive, but each can claim in its support a body of unquestioned facts of
observation. The advocates of each include men of wide experience
in the direct study of nature, and who must be supposed to have
founded their ideas upon that study, and not to have been controlled by
such preconceptions as closet philosophy is apt to engender.

The two theories in regard to the origin of mountains are correlated,
however, with certain notions concerning the condition of the interior
of the earth, which are necessarily to a great extent speculative. To
the catastrophist it is natural to conceive the crust of the earth as a
body of great rigidity and strength, resisting the force applied to it by
subterranean action until by cumulation it had become very great, and
then suddenly yielding. To the uniformitarian it is natural to conceive
the crust of the earth as in a high degree mobile, responding promptly
to all subterranean influences and reflecting them in the configuration
of its surface. These differences of view are in the main independent of
those other differences which are concerned with the thickness of the
crust, and some physicists who are disposed to assign a great thickness
to it or even to regard the entire mass of the earth as solid are at the
same time of the number who ascribe an extreme mobility to its mate-
rial.

To the catastrophist the growth of each existing mountain is a work
of the past, the present day witnessing only its decay. He does not
necessarily regard the work of mountain making as complete and look
to’ the gradual extinction of mountain masses from the present time
onward, but he at least views the present as a period of inactivity and
conceives the mountains of the future as the products of paroxysms
yet to occur. To the uniformitarian the present is, equally with the
past, an epoch of mountain building, and whether the present rate be
more rapid or less rapid than that of the past, the process is ever the
same. He therefore expects to obtain from a study of that which is
actually transpiring such criteria of judgment as will enable him to
understand the revolutions of the past.

Erosion begins with the inception of a mountain, but is at first a
slow process, because the gentle initiative slope gives to flowing water
only a small velocity, and with a small velocity its erosive power is
feeble. As the mountain rises the declivities of its sides increase and
the eroding streams have greater power; so that the rate of waste of a
mountain depends upon its height. There are other considerations

IGA
194 LAKE BONNEVILLE.

which affect the matter, and the controlling conditions are somewhat
complex, but it is true in a general way that as mountain masses grow
the rate of waste increases much more rapidly than the altitude. It was
hence argued most cogently by Powell that all large mountains are
young mountains, and from the point of view of the uniformitarian, it
is equally evident that all large mountains must be growing mountains;
for if the process of growth is continuous and if a high mountain melts
with exceptional rapidity before the play of the elements, it is illogical
to suppose that the uprising of any mountain which to-day is lofty has
to-day ceased. If, therefore, it were possible to ask of all great mount-
ains the question whether they are now growing, and obtain an answer,
a solution might be reached of the problem which has divided investiga-
tors; and for this reason great interest attaches to any answer which can
be obtained in the case of any mountain. ‘We shall presently see that
the lake vestiges help us toan answer with regard to some of the mount-
ains of Utah.

The origin of continents is closely allied to that of mountains. It is
known by the same sort of geologic evidence that every part of every
continent has been at some time submerged beneath the ocean, and that
some parts have been many times submerged, and it has been estab-
lished with equal certainty that at least some parts of the ocean have in
the ages of the past been continental. The submergence of the land
now continental has not been equable in all parts, but some districts
were flooded while others were uncovered, and vice versa. Those dis-
tricts which are at any time submerged are then subject to sedimentation,
and those which stand as land surfaces are more or less degraded by
erosion; but erosion and sedimentation both have their limits at sea level,
and have no power either to build the sea bottom into land or to sub-
merge the land. All the great changes have been produced by earth
movements of uprising and depression, and must be referred to the ac-
tion of subterranean forces either similar to or identical with those which
have produced mountains.

With reference to the rate of continental movements, there is not the
same conflict of opinion as concerning the growth of mountains, but
they are generally regarded as slow and continuous. And there are
none to question the fact that there have been notable local changes
in the height of the land since the close of the Glacial Epoch and even
some measurable changes within historic time. The evidence by which
these movements are known has been derived almost exclusively trom
the vicinity of the ocean, but there are a few inland localities which afford
facilities for their determination. The basin of Lake Bonneville is one
of those localities.

Each shoreline of the old lake was originally the tracing of a level
surface and was therefore horizontal. If it is not horizontal now, oro-
graphic movement must have intervened, and the difference of level be-
tween any two points of the same shore measures exactly the differen-
eiLpEnt.] DEFORMATION OF TIE SIORES. 195

tial movements of the two points. It is, of course, conceivable, and it
is indeed far from being improbable, that the entire basin has bodily
moved upward or downward in the same interval of time, but of such
changes the shorelines can give no proof; their evidence is limited to
the relative vertical movements of different parts.

The value of the shorelines as an orographic record was early appre-
ciated, and great pains were taken, not only during the past summer
but at every opportunity in previous years, to ascertain by the aid of
the spirit level the altitudes of the Bonneville and Provo shores at as
many points as possible. The numerous railroad surveys which now
intersect the region made it possible by running short accessory lines
of leveling to compare together widely separated portions of the coast,
and still:other comparisons were made by running levels from the
water surface of Great Salt Lake at various points of its margin to
the ancient water margins upon contiguous mountain slopes. Where
the use of the level was impracticable recourse was had to the barome-
ter, and although its determinations are fur less trustworthy they were
made with such precautions and under such restrictions that the addi-
tional information they convey cannot be regarded as entirely valueless.
The summer’s work increased the number of determinations of the
Bonneville shoreline by spirit level to seventeen, and of the Provo
shoreline to nine. In localities where no means were available for the
determination of the absolute height of the water marks, it was never-
theless frequently possible to ascertain the relative altitudes of the dif-
ferent shores, and this was repeatedly done; so that the difference of
altitude of the Bonneville and Provo shorelines is somewhat more
widely known than the absolute altitude of either.

The general results of the investigation are, first, that neither of the two
shorelines is now horizontal, and, second, that the two are not parallel;
whence it is evident that the region has been the scene of orographic
movements both during the existence of the last high stage of the water
and since the final subsidence. The detailed results are not so simply
stated, but they are too interesting and instructive to be passed in silence.

At the time of its formation every part of the Bonneville shoreline
(for example) fell within the same horizontal plane, and we may con-
céive that plane as extending indefinitely not only through the mount-
ains beyond the water margin but over the valleys filled by the water,
and as having a fixed relation to the bottom at every point. Every
orographic movement which took place subsequent to the formation of
the shoreline would have the effect of deforming this imaginary plane;
and if we were able to determine at all points the present position of
the plane we could draw a perfect picture of the deformation effected
by subterranean forces in the given interval of time. The only portion
of the plane, however, which can now be determined is that marked
by the shoreline, and our knowledge of the deformation cannot there-
fore be perfect. Nevertheless, the ancient lake had so sinuous a shore,
196 LAKE BONNEVILLE.

and its surface was so frequently interrupted by islands, that a highly
instructive restoration of the deformed plane could be made if only we
knew the present height of every part of the shoreline; and even from
the imperfect data which have been gathered it has been practicable
to obtain a rude idea of the general character of the displacement.

Tf an outline of the lake be traced on a map, and if all points of the
old shoreline which have now the same altitude be connected by a line,
it is evident that this line will constitute a contour* of the surface of
deformation. It is further evident that if a number of such lines be
drawn, each at a different height, and if their several heights be chosen
so as to form a uniform series, the lines will constitute a contour map
of the deformed surface. An attempt was made to do this.

Three maps of the lake were prepared, and upon them the data were
plotted. On the first every locality at which the height of the Bonne-
ville shoreline had been determined was marked by writing the figures
which express, in feet, the altitude of the shoreline at that point above
the water surface of Great Salt Lake; on the second the determined
heights of the Provo shoreline were similarly plotted; and on the
third the determined differences of beight between the two shorelines.
The data on the first map illustrate changes which have occurred in the
interval of time from the formation of the Bonneville shoreline to the
present day; those on the second illustrate changes which have taken
place between the formation of the Provo shoreline and the present
day; and those on the third illustrate changes occurring after the for-
mation of the Bonneville shoreline but before the completion of the
Provo. When it was attempted to draw contour lines through and
among the determined points of the third chart, it was found that the
data were so irregular that they could be satisfied by no simple system
of contours, and of the numerous complex systems which could be in-
vented in conformity with them there was no single one entitled to
preference. The result was therefore indeterminate. The chart of the
post-Provo deformation proved more tractable, and all of its data were
found to consist well with a simple system of contours drawn at vertica]
intervals of 25 feet. The post-Bonneville chart, which in the presence
of full data should represent the combined result of the other two, was
found to hold an intermediate position in facility of interpretation, ad-
mitting of a scheme of contours with vertical intervals of 100 feet. The
post-Bonneville and post-Provo charts are reproduced in Plates XLII
and XLII.

* A contour is a device for the expression of topographic forms. Conceive a hill to
be intersected by a horizontal plane; the line in which the plane meets the surface of
the hill is a contour of the surface, and has everywhere the same height. If thero
are many intersecting planes parallel to each other and separated each from each by
the same space, the corresponding contours constitute a system. It is evident that
where the slope is steep, contours will fall near together, in a horizontal sense, and
where it is gradual they will fall farther apart. When the contours of a hill aro

traced on paper they constitute a contour map. In practice the lines are not drawn
on the ground, but on paper only, as a means of expressing the form of the ground.

 
U.S.GEOLOGICAL SURVEY

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Gruner. THE iE AND TIIF PLAIN, 197

Referring to Plate XLII it will be seen that the figure of deformation
of the Bonneville shoreline exhibits at the north, in the district of the
main body of the lake, an axis of uplift, coinciding approximately with
the 113th meridian. The altitudes determined at Promontory and near
Grantsville, points which lie slightly to the east of that meridian, are
greater by about 100 feet than those along the eastern and western
shores of the old lake. The westward slope of the anticline was demon-
strated by a single station only, that near the town of Tecoma, and was
not traced farther south, but the eastward slope was traced contin-
uously southward along the eastern shore of the old lake quite to its
southern end. At the extreme southern limit of the lake, the south-
western shore of Escalante Bay, there is a rapid rise of the surface of
deformation toward the west, amounting to 200 feet in a distance of
about twenty-five miles. In the northern part of the lake the range of
altitudes, all of which were determined by spirit level, is 168 feet. At
the south, where a portion of the altitudes were determined by the aid
of the barometer, the range is 353 feet. ‘

Plate XLII exhibits in the same manner the curves of deformation
of the Provo surface and the data from which they were drawn. At
the Provo level the lake did not extend so far south as the Escalante
Bay, and no verification is afforded of the indications there given by the
Bonneville shoreline, but at the north the lines curve in a precisely
similar manner about an axis in the vicinity of the 113th meridian.
The greatest determined altitude of the Provo shoreline above Great
Salt Lake is 680 feet, at the north end of the Aqui Mountains, near
Grantsville, and the least determined height is 553 feet, at 2 point known
as White Mountain, near the town of Fillmore; the difference between
these two, or the range of all the determinations, is 127 feet.

The principal concurrent result of the two systems of measurement—
that a region in the middle of the main body of the ancient lake has in
recent times been upraised with reference to the adjacent region at the
east—finds a curious and interesting support in an entirely independent
fact. Great Salt Lake does not occupy a marked local depression but
rests upon the surface of a broad plain. Its mean depth is scarcely fifteen
feet, and only a slight oscillatory movement of the plain would be neces-
sary to decant its water into another portion. By reverting to the map
in Plate XLIII, the reader may obtain a clear idea of the form of this
plain and of the position of the lake upon it. He will see also that
the Bear River, the Weber, and the Provo, the only large streams
wnich send their water to the plain, all rise to the eastward and enter
it from the east side. That is the side of the Wasatch Mountains
and associated uplands, which in the time of Lake Bonneville as well
as how afforded the chief and almost exclusive water supply of the
basin. The sediment which accumulates in the basin is brought to it
by the tributary water, and the greater part of it is conveyed by
these large streams flowing from the east. If there were no disturbing
198 LAKE BONNEVILLE.

causes it is easy to see that the detritus would build up the eastern
side of the plain and leave the greatest depression at the west. The
normal position of Great Salt Lake is therefore in the extreme western
part of the basin, between meridians 113 and 114, and its actual position
between meridians 112 and 113 must be regarded as abnormal. To
account for it there is no hypothesis so simple and satisfactory as that
which assumes an orographic tilt of the surface of the plain—a tilt ex-
ecuted at a rate sufficient to overcome the opposing tendency of the
silt-bearing streams from the east. The position of the lake therefore
conspires with the indication of the deformed ancient lake margins to
show that the region of the eastern margin of Lake Bonneville has re-
cently undergone depression and presumably is still subsiding.

The gentle undulations of the earth’s crust which are thus exhibited
are of the order of those which have produced continents and have con-
tinuously modified their contours and limits. Indeed Great Salt Lake
is in some sense an epitome of the ocean, and its position within its
basi is as thoroughly controlled by orographic displacement as are
the greater features of the distribution of laud and water upon the sur-
face of the globe.

When these movements are spoken of as “ orographic” it must not be
understood that they are here concerned in the construction of mouunt-
ains. The greatest mountain of the district, and the one therefore to
which the uniformitarian would look for evidence of recent growth, is
the Wasatch, a massive range which forms the eastern wall of the desert.
The deformation indicated by the shorelines actually diminished its alti-
tude with reference to parallel and smaller ranges at the west, instead
of increasing it, and therefore tended to make it a less conspicuous
structure than before. There were, however, other changes in progress,
and these, as we shall see, had the effect of really increasing the height
of the Wasatch above its base.

It should be said in passing that the only growth of a mountain
with which we are here concerned is growth as referred to the adjacent
country. Itis hardly conceivable that it should ever be known whether
the summit of a mountain is at one time nearer the center of the earth
than at another, and it is a matter of great difficulty to determine the
relation in altitude which a mountain summit bears to our least variable
datum plane, the level of the ocean. And even if these relations were
known they would not determine the height of a mountain as a mount-
ain, because no eminence, however great, would constitute a mountain
unless surrounded by land of less altitude. In discussing the growth
of a mountain, therefore, we are concerned only with the relation of its
crest or its mass to the adjacent lowlands, and we must regard it as
actually growing so long as its height increases relatively to the low-
lands.

In order to understand the evidence of the recent growth of the Wa-
satch it is necessary to understand its general structure. In detail its
oILpeRT.} THE’ WASATCIL STILL GROWING. 129

structure, like that of most mountains, is highly complex, but its domin-
ating feature admits of easy statement. Before the mountain rose its site
was occupied by horizontal strata. The uplifting by which it was pro-
duced had the effect of bending these strata upon one side, but broke
them off upon the other, so that at the east the superficial strata of the
country are seen to turn up toward the flanks of the range, while no
such phenomena appear at the west. The diagram will probably con-
vey the idea more clearly than words. At A are represented the hori-
zontal strata from which the rocks of the mountain were torn away. At
B the dissevered prolongations of the same strata appear in an upturned
position. If there had been no erosion during the uplifting of the mount-
ain it would be much higher than it actually is, and the crest would
have some such position as that indicated by the dotted line. But
erosion has actually supervened, and a large share of the uplifted mass
represented by C has been worn away and deposited upon the flanks of
the range in the strata D and E. Approaching the mountain from the

   

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Fic. 21.—Generalized Cross-section of tho Wasatch Range.

west one traverses the surface of the deposit E, which is made up en-
tirely of fragments from the range, and at the point F passes abruptly
onto solid rock—the worn edges of the upturned strata. He crosses
there the line produced by the intersection of the fault plane with the
surface of the ground, and this line is everywhere marked at the pres-
ent day by an escarpment or sudden ascent, produced by the last slip-
ping of the rocks along the fault plane.

Mountain structures of this sort are not infrequent in the Great Basin,
and it is by no means rare that a definite escarpment is found at the
base of a range, recording a faulting at so recent a date that its evidence
has not been obliterated by erosion, but there is usually no manner of
fixing the date of the last movement with any high degree of precis-
ion. In the case of the Wasatch, however, our information is concise.
The slopes interrupted by the escarpment are not simple alluvial slopes
or rock slopes carved by subaerial agencies, but are slopes characterized
by the peculiar sculpture of the waves; and the phenomena show not
200 LAKE BONNEVILLE.

only that the last uplift of the Wasatch took place after the forma-
tion of the Bonneville and Provo shores, but that the water of Great
Salt Lake has not since been even fifty feet higher than it is at present.
It is therefore demonstrated that an actual uplift of the mountain
occurred at so recent a date as to leave no reasonable suspicion that its
growth has now ceased.

The amount of displacement along this fault plane is not great, but
it is probably greater than the amount of coincident erosion of the
mountain top; so that it is reasonable to believe that the Wasatch is a
greater mountain now than it was during the existence of the Bonne-
ville Lake. Where the range is highest the amount of recent faulting
at its base is from fifty feet to seventy-five feet, and it diminishes ir-
regularly in either direction—the fault being traceable from the town of
Willard at the north to that of Levan at the south, a distance of one
hundred and thirty-five miles.

SUMMARY.

In brief, the work of the year may be said to have completed the
demonstration of the following conclusions:

1. The climatic episode of which Lake Bonneville was the expression
consisted of two humid maxima, separated by an interval of extreme
aridity. The second maximum was the more pronounced; the first the
longer.

2. The time elapsed since the close of the Bonneville epoch has been
briefer than the epoch, and the two together are incomparably briefer
than such a geologic period as the Tertiary.

3. The period of volcanic activity in the Great Basin, which covered
a large share of Tertiary time, continued through the Quaternary also,
and presumably has not yet ended.

4. Such earth®movements as are concerned in the molding of conti-
nents had not ceased in Western Utah at the close of the Bonneville
Epoch, and presumably have not yet ceased.

5. The Wasatch Range, the greatest mountain mass of Utah, has
recently increased in height, and presumably is still growing.