ST. JOHN.] HOBACK CANON RIDGE.. 181 
plated by the Jura. The “red beds” appear in force on the west side 
of the canon above, exhibiting a thickness of above 1,000 feet, dipping 
westward, in which direction they merge into the broken outlying slopes 
of the Hoback Cafion ridge. North of the Hoback, as before mentioned, 
the continuity of this ridge is much broken by the streams here descend- 
ing from the Gros Ventre Mountains, and it is not improbable that, in 
its geologic structure, it is also complicated by proximity to the latter 
mountain range. 
The valley of the tributary separating the above outlying ridge from 
the main ridge south of Hoback Cafion is generally narrow and fre- 
quentiy walled in by precipitous rocky slopes. ‘The narrow intervale 
expansions show well-defined terraces, and the stream-bed is paved with 
water-worn fragments of red sandstone and drab limestone, derived from 
the environing Jura-Trias deposits. However, on gaining the Hoback, 
the Quaternary deposits which fill the valley-bed are largely composed 
of Archean and Paleozoic débris, from the Gros Ventre Mountains on 
the north. These materials extend through the canon, where they are 
intermingled with the débris fallen from the adjacent cliffs and washed 
down the short gulches that penetrate the ills on either side. There 
ean be little doubt that during the time of the Quaternary period this 
gorge was filled with drift materials, remnants of which—boulders of 
various kinds of rocks—still being met with high up on the adjacent 
mountain slopes. Subsequently these deposits were to a great extent 
swept away, and in the narrow portions of the caiion fhe talus slopes 
consist almost entirely of the sliding, angular rock fragments fallen from 
the limestone and sandstone cliffs, over which the trail, in places, has 
precarious footing. From time immemorial the Hoback Cation has been 
used as a highway, communicating between the Upper Snake and Green 
River valleys. Many well-beaten trails converge at the upper entrance, 
whose antiquity may be inferred from their distinctness in spite of their 
comparative present disuse. Its importance in this respect is, indeed, a 
matter of historic record, reaching back to the first decade of the cen- 
tury when the region was first visited by the adventurous fur-traders. 
About midway of the Hoback Cafion the hills recede, inclosing a pretty 
little park clothed with verdure, shrubs and trees. On the north side 
it is terraced with high benches, in which Mr. Perry discovered some 
interesting deposits of gypsum. The gypsum, so far as investigated, 
seems to occur in isolated patches included in the loose débris of which 
the terraces are composed, recalling the tufaceous deposits of springs. 
In texture and color it varies from compact to porous, pure white to 
grayish or soiled white, and apparently forms quite extensive deposits. 
That examined appears in the steep slope of the terrace near the brink, 
at an elevation of about 115 feet above the stream, and shows a thickness 
of 4 feet. Lower down, or just within the lower entrance to the caiion, 
a powerful sulphur spring issues along the north bank at the edge of the 
water for a distance of 30 or 40 yards, emitting the odor of sulphureted 
hydrogen. The spring water is not unpieasant to the taste; the tem- 
perature at 7 a. m. (7th August) indicated 47° I. The spring is seated 
immediately over an anticlinal fold, whose axis is here composed of Car- 
boniferous—possibly Niagara—limestone. In favorable situations, the 
pebbles in the way of the spring currents are coated with a sulphur pre- 
cipitate, and the inflowing spring water discolors that of the river for the 
distance of several hundred yards below with a strip of beautiful green. 
This unquestionably is the sulphur spring described by Rev. Samuel Par- 
ker,* who journeyed down the Hoback in 1834. It may be well to remark, 
* Journal of an exploring tour beyond the Rocky Mountains. Ithaca, N. Y., 1844, 
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