180 REPORT UNITED STATES GEOLOGICAL SURVEY. 
The nucleus of this outer ridge is apparently almost exclusively made 
up of Mesozoie strata, excepting ga small angle in the vicinity of the junc- 
tion of this south affluent with the main stream, where strata of later ~ 
date compose its bulk. Structurally, it presents a somewhat variable 
present condition that was determined by a sharp fold in the older strata, 
which locally exhibit the appearance of a regular anticlinal. In the 
southern portion, 6 or 8 miles above the mouth of the stream, the ridge 
shows a monoclinal structure, the stream occupying a sy nelinal from 
which the strata rise to the eastward into the narrow, picturesquely- 
weathered crest, 1,000 to 1,200 feet high. The east side is sharply broken 
down, and on the ‘upturned edges of “the nucleal strata rest the uncon- 
formable Tertiary deposits, dipping off to the eastward. Whether the 
condition of things here represents a fault with down throw on the east, 
or is attributable to denudation along the shore line of the Tertiary sea, 
was not clearly apparent. In the latter case the tilting of the Tertiary 
deposits would indicate a late-continued elevatory movement within the 
area of this western mountain border of the Hoback Basin sufficient to 
account for the present position of the Tertiary deposits which slope off 
into the basin at an angle of variable steepness. 
Hight miles south of the Hoback this ridge is made up of hard red- 
dish- ‘buff sandstone and brecciated silicions beds, steeply tilted and 
rising along the crest into picturesque, ruin-like crags. Two or three 
miles lower down the stream, the west slope is flagged with drab, spar- 
seamed limestone, containing a small Ostrea and Pentacrinites. These 
beds dip about WNW. at angles of 35° to 65°, and are overlaid by lime- 
stones and indurated calcareous shales containing abundance of Gryphea 
calceola, which, however, are soon concealed beneath the débris lower in 
the slope. Below the latter point the reddish or flesh-colored Triassic 
sandstones descend lower in the west slope, and as the course of the stream 
bears more to the east it crosses these beds, cutting a narrow gorge in 
which their anticlinal structure is well brought out, Below the gorge 
the valley is less confined, and is bordered on the east by beautifully 
rounded hills based on the soft gray deposits—alternations of sandstones 
and shales—of the Tertiary, which continue thence below the confluence 
of the Hoback. The latter deposits show a thickness of perhaps 1,009 
feet, dipping eastward at an angle of 30° to 45°, and at the confluence 
of the streams forming a low outlying hill on the west side of the valley. 
Similar remnants occur below the junction for some distance, forming 
benches low in the slope resting upon the westerly-dipping Triassic red 
sandstones, which form the crest of the west side border ridge. The 
Tertiary slopes are partially wooded with conifers, as also are the more 
rugged Triassic acclivities. 
The main Hoback here pursues a northwesterly course, and a mile or 
se below the junction it has formed a narrow passage across the Triassic 
monoclinal ridge. The typical red sandstones show picturesque expos- 
ures, dipping west at an angle of 35°, the outlying ridges on the east 
being made up of the Tertiary deposits. In the angle formed by a con- 
siderable inflowing branch from the north, a high castellated mass of red 
sandstone fills the east side of the valley, sharply turning the stream 
west. The west slope of this hill is faced with heavy ledges of red 
sandstone, including a drab calcareous or limestone deposit, steeply in- 
clined westward. The summit is crowned by apparently nearly hor- 
izontal ledges of the same character, as though the strata had been par- 
tially severed and broken down or dragged on the west side of the fold, 
leaving the crest intact. In the west side of the narrow valley the strata 
again rise, but a little lower down they are seen to form a perfect arch 
