aiARViKE.] GEOLOGY NOXCONFOEMITY AT HOT SPRINGS. 167 



tween it and the volcanic breccia, there occurs here a thickness of about 

 2,700 feet of sedimentary rocks lying above the breccia bed. The ravines 

 from the north cut deep into these terraces, breaking them up into promon- 

 tories with squarish fortification-like fronts facing the river. Upon the 

 south side of the river these features are far less defined, and here only 

 thelowerand softer beds occur, while the northward dip increases. The 

 valley, after passing the breccia bed, is quite open, the river being lined 

 with 'much beautiful bottom-land. Below the gate-way some of the lava 

 appeared to outcrop low down near the inver, but its relations were not 

 examined. 



These terraced beds are of the characteristic lignitic group, and are 

 very different lithologically from the undoubted Cretaceous beds lying 

 below the breccia. Nearly all the exposures here show them to be sand- 

 stones, the more prominent ones, or those which give the terrace-form 

 to the eroded beds, being mostly grits, quite coarse, often becoming con- 

 glomerate, not very firmly cemented, and composed almost wholly of 

 granitic and metamorphic dSbris, (except that the mica is naturally ab- 

 sent,) while feldspar crystals, sometimes retaining much of their form, 

 occur. The color is mostly somber dark brown, though some are quite 

 white. Some finer and more compact beds occur, with occasional fossil 

 leaves. 



In descending the Grand, the terraced beds on either hand are found 

 to become slightly inclined to the northeast, amounting perhaps to about 

 10°, the river thus passing down through the lower beds as before it 

 passed up through these, until at about four miles in a straight line 

 from the upper gate- way, another and somewhat similar passage is found 

 by which the river again breaks through a ridge of precisely the same ma- 

 terial as before. It is, in fact, the same bed again appearing to view from 

 beneath the same lignitic sandstones, the strike being about northwest 

 and southeast, but the dip about 15° to the northeast, the bed there- 

 fore being folded into a synclinal form, the east side being bent down- 

 ward more abruptly than the western side. As before much of this 

 series is massive, or wholly indefinitely bedded, and some compact lava 

 occurs, as if of distinct lava-flows. The latter seems to be doleritic, 

 crystals of augite being quite frequent, though some is more basaltic, 

 being fine, and quite homogeneous. Most, however, is of a distinct 

 conglomerate and breccia, some very coarse, of pebbles like the accom- 

 panying lava, many scoriaceous, while much is of fine material, finely 

 and evenly bedded. Their total thickness was estimated at about 800 

 feet at this point. The accompanying sketch. Fig. 14, of an exposure 

 about half a mile north of this gate- way was made by Mr. Holmes, 

 and shows the distinct bedded nature of this volcanic ash, &c. 



THE ^'O^NTCGNFOKMITY AT THE HOT SPEINGS, MIDDLE PARK. 



Passing through the short break by which the stream cuts through 

 this ridge, the w^estern edges of its gently eastward-dipping beds are 

 found extending northwest and southeast as a continuous line of black 

 palisades which look dow^n upon valleys tributary on either side of the 

 Grand, that at the south being wider and flatter than the one from the 

 north. 



Eegarding for a moment the section found immediately along the 

 Grand, (see Plate III, section 1,) there appears above the alluvium on the 

 north side of the stream, and a little west of, and nearly parallel to, the 

 breccia ridge, a hog-back like ridge of sandstones w^hich dip at an angle 

 of 25° or 30° northeast below the breccia. Some baculites were found 



