66 Scientific Intelligence. 
west. ing from the authetn plateaus southward to the Colo- 
cigs a wide area of Eocene Tertiary is first passed ; then bands, 
n succession, of Cretace ait Jurassic, Upper Trias, ‘Lower Trias, 
(Shina aetiatis en p), and Carbon iferous 
The youngest group in he series clearly carne out (the rele 
nary excluded) is thus the Eocene; and it would be the 
formation generally were it not for the erosion that has taken ‘pikes 
and still more for the covering of igneous rocks. These Eocene 
beds are rae of an extended lacustrine formation—as first recog- 
nized b . They are described as 5,000 feet thick around 
the Blackie of of the Uintas and southern Wahsatch, and as thinning, 
outward from these mountains, to nearly or quite 2,000 feet 
Awapa and Fish-lake Plateaus on the the great central 
Sevier Plateau, ~ the Tu shar and Markit Plateaus on the 
oldest, and the dolerytes, but as in alternating beds in some 
places with the last. In the Awapa and Aquarius Plateaus, the 
trachyte shows a thickness, in some of the profound gorges, of 
3,000 feet. The volcanic eruptions are stated to have begun in 
the middle Eocene, and a few of the foci are still distinguishable. 
The basaltic eruptions in some places look, “so far as appearance 
is concerned,” they “might have been erupted less than a 
century ago.” Beside es the eruptive beds, volcanic conglomerates 
are widely poate zee covering an area of 2,000 square 
miles, and e parts 2,500 feet thick. In some places 
they have den so vihunes d as to lose their fragmental character, 
and become in appearance closely like true eruptive rocks (a fact 
which has been observed also in the Andes and in Mexico). But 
o the voleanic rocks and volcanic action and its causes, the 
reader is referred to the Report. 
e disturbances in the plateau region have resulted in a gen- 
eral uplifting, and also in monoclinal flexures, and in fractures 
and faults; and the faults are mostly in the line of monoclinal 
uplifts, as brought out by Powell in his déacription of the Colo- 
o region on the South. The flexures and faults, as is well 
illustrated in the Atlas, have approximately a north-and-south 
course, and are, in part, a continuation of those of the Colorado 
region on the South. The “Hurricane fault” has its southern 
limit at some undetermined point in Arizona, south of the 
Colorado, and, at its crossing of the Grand Cafion, it is the 
line of a displacement of 1800 feet. It is the western bound- 
