BT.joHN.l BLACKFOOT EANGE SECTION. 347 



350 S. by W. 35° K, varying? to an east-southeast and Avest-northwest 

 course, and inclined at various angles to the north and southward, the 

 drainage generally followiug lines corresponding to, and in many in- 

 stances dei)endent on, the strike of the beds, or both. The southern and 

 southwestern portion of the area is comi)osed of Jurassic deposits, con- 

 sisting of gritty limestones, indurated arenaceous beds, and variegated 

 red and chocolate colored shales, certain layers being charged with an 

 abundant and clmracteristic fauna. These deposits, which make up a 

 vertical thickness of several hundred feet, are here thro\^ii up in a great 

 fold, the southwestern flank of which extends to the west of the Black- 

 foot, as mentioned on a preceding page, where that portion of it which lies 

 within the present district is buried beneath the late Tertiary, or Lake 

 beds, and the volcanics. Immediately the well-determined Jiu-assic fos- 

 siliferous beds which appear in the steeply-inclined northern flank of the 

 fold are left, a belt of above a mile across is so enveloped in superlicial 

 detrial material, intermingled with pinkish trachytic debris, as greatlj' to 

 obscure the underlying basis structure. But from such data as the few 

 and more or less obsciu-e exposures met with in this belt reveal, it is ap- 

 parent that it embraces the site of extraordinary disturbance, the harder 

 ledges, consisting of limestones and quartzose sandstones, with traces 

 of more extensive interbedded deposits of red sandstones and sandy 

 shales, are inclined at steep and varying angles, and in i)laces tilted past 

 the vertical or wedged in between sharp synclinal flexures. About two 

 miles north of the axis of the Jurassic fold, the southern foot of the as- 

 cent to a high dominating point is mailed by a heaA^ ledge of light-drab 

 and flesh-colored, siliceous, brecciated limestone, containing traces of 

 indeterminable fossils, and dij^ping 00°, S. 20° W. In the saddle and caQ- 

 adas which drain in either direction, east and west, deep-red gritty clays 

 appear, and in the ridge to the south a short distance, several ledges of 

 thin and heavy-bedded gray limestones, associated with brown, lamin- 

 ated, earthy, indurated layers, both of which show obscure traces of fos- 

 sils, Ceratites, &c., occur, steeply dipping to the north, or vertical. The 

 outlying heavy limestone ledge is succeeded on the north by a still 

 heavier pale reddish-buff siliceous deposit, which rises in gradually de- 

 creasing steepness up into the plateau summit, which abruptly termin- 

 ates in a parapet of clinking, fragmentary, pinkish-gray siliceous lime- 

 stone, dipping S. 38° W., at an angle of 45° to 50°. The northern face 

 of the little plateau falls quite rapidly over a series of sparsely wooded 

 benches, in which successively ajjpear ledges of gray, siliceous, and cherty 

 limestones, with small Zaphrentis and iiyringopora, crinoidal remains, 

 Productm semireticulatus and P. longispinus, the beds dipping 45°, S. 20° 

 W. The latter beds, at least, pertain to the Carboniferous, and the few 

 fossils observed belong to species prevalent during the later period of 

 that age. The detail section of the strata above alluded to, commencing 

 at Station XIII ridge, and thence carried northward to the higher Car- 

 boniferous ridge, is as follows : 



Section north of Station XIII ridge. 



a. Brown, shaly, indurated, fine, areno-argillaceous deposit with 

 dendritic markings, with thin layers of brown chocolate-gray limestone, 

 sometimes s])ar-seamed, aud containing a snmll terebratuloid shell and 

 I>isvi)iaf Api)arently a heavy deposit, 300 lector more in thickness. 



b. Brown-gray, thin-bedded, spar-seamed limestones, with intercalated 

 thin sandy layers, forming a heavy ledge in the crest of Station XIII 

 ridge, oi)posite Staltiou XII, and plating the northern slope in places j 



