DAVIS: THE PLATEAU PROVINCE OF UTAH AND ARIZONA. 47 
other hand, there must be frequent minor lapses of continuity, for the 
thin sandstone beds are certainly more common on some slopes than on 
others not far away at the same horizon. It should be noted in this 
connection that no one yet has carefully determined the degree of con- 
tinuity that may prevail in the deposits of overflowing aggrading rivers. 
The higher members of the shales and the whitish calcareous beds 
show fewer variations of structure than those beneath. They are suc- 
ceeded by fifty feet or more of inconstant deposits that vary from paper 
shales to cross-bedded sandstones, increasingly changeable in composition, 
texture, thickness, and color. Some of these upper sandstone beds 
wedge out from five feet to nothing in a distance of fifty feet. Then 
come the capping bluffs of variable brown sandstone from forty to sixty 
feet or more in thickness, frequently of even texture and massive beds ; 
again showing pronounced cross-bedding on a large scale. In the well- 
known butte that forms so conspicuous a landmark north of the town, 
there are local deposits of a bluish clay, twenty feet or more in length, 
yet hardly an inch in thickness, contained in the sandstone. In spite 
of the strength frequently attained by these capping beds, and in spite 
of the bold face which their outcrops often possess, the bluffs which the 
outcrops form are by no means continuous. They occur chiefly in prom- 
ontories and on isolated buttes, along the margin of the less dissected 
upland that here borders the valleys of Green river and its larger 
branches. The re-entrants between the promontories are frequently of 
evenly graded slope without any strong capping sandstone bluff. In 
other districts of the west, the continuity of a rimming bluff formed by 
a hard horizontal layer as it contours around spurs and into ravines is of 
common occurrence, and for that reason the discontinuity of the bluffs 
around Green river very strongly suggests the discontinuity or at least 
the great variability of the bluff-making sandstones. Thus interpreted, 
the bluffs of the promontories and isolated outliers must mark local 
thickenings of the sandstone in the mass of weaker shales. It seems 
evident that if the cardboard shales are accepted as the deposits of a 
lake, the variable bench — and bluff— making sandstones must be of 
some other origin. 
BripGER AND VERMILION CREEK TeRtTIARIES. — The Union Pacific 
railroad between Green river and Weber canyon crosses broad areas of 
the Bridger and Vermilion creek formations. Natural outcrops are 
abundant for much of the way, and many artificial exposures are seen in 
the cuts along the track. Observation from an express train cannot be 
detailed, but it suffices to prove that the strata of these formations often 
