, 1891-07-08

DOnltVllIc. IuIS, III SOliCAhl ONblihS3 49,
lldely pear-shaped, but its Shore-line was
very irregular, IL succession Of jutting head
lands and deep bays its surface also was
broken with islands. Its area mcaSur-
ed about 1880 miles, not much less than
that Of Lake Huron This is now q
region Of arid deserts, spotted here ana
there with a salt marsh or a lagoon, ana
diversified by the Great Salt Lake and two
Others Of smaller size. The greatest dcptl
was originally 1850 feet, for the Great Salt
Lake does not exceed 90 feet in any part.
Then the waters Of Lake Bonneville found
an outlet at the northern end, not Tar away
from the mouth of the Bear River. when Is
now the principal attiuent OF the OalC Lake.
The rainfall then in the northern part OF Tue
Great Basin must have been much heavier
than it is now as it diminished Lake Bonnie
vile contracted in size and increased III
sadness. The annual rainfall III his DISTRICTS
now ONLY about Z inches, while over the region
between the Appalachians and the MlsSIs-
SipDi it is 43incheS. In the latter the aver
age moisture III the air is about 90 per cent.
of eaturatiOn, in the former 1t is only 10;
while the evaporation from the surface OF
Lake Michigan is only % inches per annum,
for the Great Salt Lake it amounts TO 81
inches. The leIel Of the water III the latter
is subject to oscillations, dependent partly
on variations in the rainfall, partly on inc
results Of extended cultivation, ana appears
likely in the future to fall somewhat OeIoW
its present height.
In the disappearance of the ancient lake,
epOchs-sOmetimes perhaps rather lOn9-ot
stability appear to have aIternated with
eras of change, at any rate, shore-cIIifS,
terraces. spjts, and bars Of dCtrltuS are
very distinctly grouped at intervals above
the present water level. Owing to lhe
scanty rainfall and the absence, until late
wears of any attempt at cultivation, these
natural features are preserved Win unusual
distinctness. In the admirable plates Oy
which the memoir is illustrated, we can see
the enclosing hills, bare and arid, but fur
rowed into a thousand gulleyS by the tran
sient storms of, a myriad years; the wave
WON cliffs which overlooked the margin OF
the vanished lake; the long shelving slopes
which formed it's bed the water worn
dlbris, here accumulated in q long SPIT, ana
indicating the general set OF the waves; mere
piIed uDi in a bar, which now runs, like a
railway cm~bankmcnt, from hPadland to
hcadland across the opening Of bay. Inc
nlates of themselves are an object lesson III
physical geography.
The origin Of the basin OF Lake Bohne-
Vile, as of all other large lake basins, Is
individually. as Mr.. Gilbert points ont,
reformation of the earth's crust, or djoStpo-
pLism as he proposes to call it. But there
is evidence to slloW-and this is q point OF
much intcreSt-that during the process OF
desiccalion, this crust has not renamed
absolutely at rest; these 'bench marks
afforded by the large margins have under
gone movements which are not uniform Ill
amount. They are ssfOund, on examination,
to exhibit variations amounting III some
cases to about $50 feet in altitude. Faults,
also, may be traced for considerable DIS
tanoes, which are later i'll date than the
desiccation of Lake Bonneville. These III
places are made very distinct by scarpS,
crossing lines of terraces or alluVIal fans,
and facing outTards towards the lower
ground. These faults, however, do not maj.
cate any great displacement. The maxi
mum throw does not exceed about ~ feet,
and it is often less. Certain localities also
nave been disturbed by volcanic eruptions.
These have occurred before, during, and
since, the epoch of the greatest extension OF
Lake Bonneville. Orators of scorla, as we'll
as flows of lava, remain as monuments
the former occasionally three OF four hun
dred yards in diameter, the latter sometimes
a little more than three miles long the ma
terials are all basaltic. Rhyolltic laVas
also occur in the region, but these are long
anterior in date to the epoch OF the lake.
Organic remains are not common III the
marIs and other deposits of the OLD lake