512 Recent Literature. | May, 
moderate depth, but the Mesozoic beds were all shallow-water 
deposits, and they sank as rapidly as they accumulated. 
“ Near the close of the Cretaceous, signs of the coming revo- 
lution make their appearance. The waters became brackish, in- 
dicating a restricted access of the ocean. At the close of the 
Cretaceous important disturbances took place, and portions of 
the province were uplifted and denuded. These were again sub- 
merged, but the new conditions differed from the old, for the new 
deposits (Eocene) laid down unconformably upon the Cretaceous 
and Jurassic are of fresh-water origin, indicating that a great lake 
was formed. The extent of this lake corresponds very nearly 
with that of the Southern Plateau province itself, but not exactly. 
Near the Middle Eocene began that slow action which has gra 
ually elevated the western portion of the continent, and which 
has prevailed until a recent epoch.” i 
During the Tertiary, erosion went on continuously, the thick- 
ness removed from some large areas amounting to about oe 
feet, and much the greater part of this denudation was probably 
accomplished by the close of the Miocene. _ i l 
“The Colorado river appears to have originated in very ¢ar y 
Tertiary time as the outlet of the great Eocene lake, and ie 
sisted in its course ever since. It has been the main Siig oe 
which the waste of the province has been carried to the fore 
At its beginning its bed lay in Eocene strata, and as the lan il 
it cut down its channel by corrasion, severing in ee: 
the beds of the Mesozoic and Carboniferous systems. Tha ie 
tion of it which constitutes the Grand and Marble canons 
afion represents oniy 
amount in Kaibab. The present Grand te into the Archea® 
the corrasion through the Carboniferous an ; ly when 
The older corrasion of superior beds becomes manifest rel been 
we restore, in imagination, the Mesozoic strata which i Grand 
denuded from the vicinity of the chasm. The apse one 
cañon, therefore, is the work of late Tertiary and Q 
‘ : sai xact 
time. Although we cannot fix with pareu p eds, we may, 
och near 
Ra z iocene.” 
ginning of the Pliocene or close of the peor besides ar 
some of very recent date. After describing the ana 
Mt. Trumbull and other masses, which are much ich Jook “3 
tion is then drawn to the fields of recent basalt, whi irty 
fresh as any coulée of Vesuvius ejected twenty Ce mpared with 
ago.” Plate xx represents one of these fields. ‘® ns are large 
the other later eruptions of the Uinkaret, its dimensi ith blocks of 
the ave It entire surface is covered W! very much 
pumice of the most delicate kind. It has a texture 
ions of ore i 
