iiAKVLNE.] GEOLOGY VALLEY OF THE LOWEE GRAND. 177 



coDglomerates strangely resemble some of the lignitic conglomerates in 

 general characters, but lake-beds at this point, being naturally made up 

 of debris from the granites and lignitic beds adjacent, might readily re- 

 semble the latter. 



A little farther down the river again approaches the red granite, 

 which rises ruggedly to form its northern bank, the lake-beds being 

 again confined to its southern side, and here of a rolling rather than of 

 a terraced character. The granite appears rather smoothly surfaced, 

 and is cut through by the caiion of Corral Creek, which flows from the 

 lignitic area ui)on the north. Nearly opposite its mouth, and west of 

 the mouth of the Williams Eiver, is a high hill with a great white ex- 

 posure, so characteristic of the lake-beds, on its steep, north face. Near 

 its eastern base are evidences of formerly existing sulphur springs. 



After leaving the Corral Creek granite area the river-bottom is often 

 a half mile wide, bounded on either side by a terrace of about 80 feet in 

 elevation, excei)t where the latter has been cut back by erosion, when 

 the rise is often 150 feet, or to the summit of the second and higher ter- 

 race, direct. The latter terrace surface, rising in more gentle slopes to 

 200 or 250 feet, forms the general level between the Grand and lower 

 Troublesome Creeks. From it here rises a rocky knob composed of 

 granitic gneiss and dark irregular gneiss. South of the Grand, also, are 

 two hills showing granitic outcrops, the lake-beds stretching past them 

 southward, their relations to the Upper Cretaceous or lignitic beds of the 

 north end of the Williams Eiver Mountains not being examined. Ex- 

 posures of highly cross-stratified sands are here exposed on the south 

 bank of the Grand. Farther down the river the well-defined terraces, 

 each of about 80 feet in height, are quite continuous. On the north side 

 a few small knobs of metamorphic rocks protrude through them, while a 

 quite large mass of the same (Station LXVIII) rises on the south, close 

 to which the river runs, with steep slopes rising to it. A spur of the 

 same runs quite to the junction of the Blue and Grand. Here a large 

 flat alluvium area spreads out, lying, when visited, only about five feet 

 above the river, and probably subject to inundation in very wet seasons. 

 Passing it, the river breaks through the Lower Cretaceous rocks lying 

 up against the eastern granite slopes of the Park range and enters its 

 impassable caiion through the same, carrying with it all the drainage of 

 the Park. The rapid deepening of this canon will probably ere long 

 retrieve the rich alluvium bottoms just above from serious inundations. 

 Nearly all the terraces of this region adjacent to the Grand are covered 

 with debris of metamorphic rocks, and sustain a poor vegetation of sage- 

 brush, with very little grass, though the river-bottom appears very fer- 

 tile. In the softer lake-beds much alkali is present, and the ravines are 

 boggy. Though obscuring the underlying rocks as they do, enough is 

 visible to show that the zone along the Grand is one, essentially, of the 

 archsean rocks. Taken in connection with the sedimentary rocks both 

 to the north and south, it would seem to be a gentle anticlinal, with an 

 east and west axis, extending from the Hot Springs to near the mouths 

 of the Blue and Muddy, with the overlying rocks swept away by erosion 

 and replaced by the later lake-beds; while the apparent continuity of 

 the mass with the granite of the Hot Springs would suggest that possi- 

 bly the fold throughout was of the same age as the Hot-Springs fold, 

 viz, post-Cretaceous, but pre-lignitic. The lake-beds so cover up the 

 edges of the adjacent formations that the relations between them are 

 readily seen, but ravines might be found exposing suflBcient to really 

 determine these relations and the true nature and age of the fold. As 

 before mentioned, several sulphur springs occur a little east of the Lower 

 12 G s 



