358 
NATURE 
[ Feb. 15, 1883 
Capt. Dutton may be congratulated on having accom- 
plished this task with as large a measure of success as pro- 
bably was achievable. Without entering into stratigraphi- 
cal details he addresses himself to the problem of the 
origin and history of the erosion that has converted the 
level rock-platforms of the Colorado River into their 
present profoundly trenched condition. Sketching briefly 
but clearly the general geographical features of the 
region and their relation to the underlying geological 
structure, he presents the reader with a series of pictures | 
of the various types of scenery. He shows how every- 
where the evidence arises of vast denudation. Not only 
have the wide valleys and deep gorges been excavated, 
but an enormous amount of material has been worn away 
from the broad rocky terraces. From the high plateaux 
of Utah the Mesozoic and Tertiary formations descend 
by a succession of broad terraces like a giant staircase 
to the platform of Palaeozoic rocks. Capt. Dutton gives 
reasons for his belief that the strata which end at the 
cliffs of these successive terraces once extended over the 
whole of the Grand Canon district, and he estimates 
the amount of rock thus removed to have averaged 
probably 10,000 feet in thickness over an area 13,000 
to 15,000 square miles in extent. He bases this esti- 
mate partly upon the obvious continuity of the strata, 
and the improbability that they could have ended 
off upon the Carboniferous platform; partly upon the 
evidence of displacements whereby Paleozoic rocks, 
formerly buried at least 10,000 feet below the sea-level, 
under an accumulation of sediment of that depth, have 
been again uplifted into the lofty plateaux of the 
Colorado ; partly upon an argument from the history of 
the drainage-lines of the district. In this last argument, 
developing the views so forcibly expressed by Jukes many 
years ago for the rivers of the south of Ireland, and more 
recently applied by Powell to the stupendous illustrations 
in the Colorado basin, he shows that the present courses 
of the rivers are so entirely independent of structural 
features, that their position is inexplicable save on the 
interpretation that when the streams began to flow these 
features had not revealed themselves. He thus smoothes 
over the faulted Carboniferous platform, piles over it a 
covering somewhere about two miles thick of Mesozoic 
and Tertiary strata, and makes the rivers begin their first | 
erosion on the surface of this covering. The faulting, | 
plication, and uplifting have taken place subsequently ; 
but meanwhile the rivers have kept their courses, inces- 
santly sawing their way downward into lower layers of 
rock, and across the dislocations and folds that subter- | 
ranean disturvance might throw across their path. No 
thoughtful student of this subject can refuse his assent to 
the solution of the problem so well worked out. 
In tracing the geological history of the canon region, 
we find at the bottom of all the visible strata, a founda- 
tion of ancient crystalline Archzan rocks, and also 
crumpled and broken masses of stratified formations, 
referred with more or !ess confidence to the Silurian and 
Devonian periods. The disturbance and extensive denu- 
dation of the older Palaeozoic masses had been effected 
before the lowest of the vast conformable ‘series of forma- | 
tions in this region began to be deposited, for the latter 
lie upon the upturned edges of the former, as on a plat- 
form—an impressive feature in the scenery. Continuous 
| to that distance below it by the end of the period. 
sedimentation began some time in the Carboniferous 
period, and appears to have been carried on with no 
sensible break up to the close of the Eocene period, until 
a total depth of at least 15,000 feet of sediment had accu- 
mulated. The Carboniferous portion is estimated at a 
thickness of 4500 feet, the various Mesozoic formations at 
g0oo or 10,000, and the portion of Eocene lacustrine beds 
deposited were 1000 or 1200 feet. 
Capt. Dutton calls attention to the remarkable uni- 
formity and persistency of the lithological characters of 
each formation, while at the same time there is great 
diversity in those respects between the strata of different 
platforms. By far the larger proportion of the whole 
mass of conformable strata consists of sandstone, pre- 
senting on successive horizons the most extreme contrasts 
of structure and colour, for they consist along certain 
platforms of adamantine quartzite, in others of massive 
cross-bedded sand-rocks, while they graduate also into 
shales and these into marls. It is this alteration of strata, 
showing very different degrees of permanence, yet each 
retaining its normal characters over vast areas, that 
affords the key to much that is most characteristic in the 
scenery of the region. The limestones are almost wholly 
confined to the Carboniferous system, where they occur 
both in the lower and upper divisions. 
Another significant feature brought out by the survey 
is the evidence that sedimentation went on nearly at sea- 
level during the whole of Mesozoic time throughout the 
Canon province. As the Mesozoic strata are go000 or 
10,000 feet thick, it is obvious that the sediments which 
were at or near the sea-level at the beginning had sunk 
We 
have here, therefore, a consecutive series of shallow-water 
deposits not much less than two miles in vertical thick- 
ness. The Cretaceous rocks which form the uppermost 
division of this series are from base to summit banded 
with seams of lignite or coal, and layers containing marine 
mollusca. They vary in different parts of the province 
from 3500 to 8000 feet in thickness. At the close of their 
deposition, those movements appear to have begun which 
have culminated in the elevation of the sea-floor into the 
elevated plateaux that now form so prominent a feature 
on either side of the watershed of the continent. 
With the advent of Eocene time the shallow sea-floor, in 
which sedimentation had been so continuous during the 
whole of the Mesozoic ages, began to be converted into 
wide fresh-water lakes. The Tertiary history of Western 
America is in large measure a record of the formation, 
duration, and effacement of these lakes, as the land 
gradually increased in elevation. In the plateau country 
| the Eocene lacustrine deposits range from 1000 to 5000 
feet in thickness. Great as this accumulation is, it 
unquestionably took place in comparatively shallow 
water over an area that was generally rising, yet was 
locally sinking, so that the lake persisted, and remained 
shallow ; for its depth was reduced by the deposit of 
sediment as fast as it was increased by subsidence. The 
waters appear to have dried up from south to north, and 
finally disappeared somewhere in the area of the Uinta 
mountains. 
It was on the floor of this desiccated lake that the 
drainage system of the Colorado river began, somewhere 
about the close of the Eocene period. During the vast 
