224 BULLETIN UNITED STATES GE0L0GICA7, SURVEY. [VoLY. 



Eiver side of the divide the stream becomes comparatively large at once, 

 being fed by many springs and a great deal of marsh." In figure 3, 

 plate III, I give a copy of Captain Jones's map of this locality. 



During the past season, the writer, on his return from the Yellowstone 

 Park, passed over this divide, and made a somewhat careful study of it. 

 The chart, which was sketched on the spot by Mr. W. H. Jackson, shows 

 the exact character of the drainage. 



This pass is located about longitude 110° 00' and latitude' 44° 05'. 

 Atlantic Creek is a branch of the Upper Yellowstone Elver. The party 

 with which the writer was connected passed up the east side of the Yel- 

 lowstone Lake to the mouth of the XJi)per Yellowstone Eiver, and thence 

 up the valley of that stream about thirty miles to what may be called 

 the Three Forks, near Bridger's Lake. The east fork bears the name 

 of Atlantic Creek. From the Three Forks the party passed up the val- 

 ley of Atlantic Creek to the southwest, for the most part over a grassy 

 valley, which was enclosed between vertical walls of volcanic breccia 

 1,000 to 1,200 feet in height. This valley is purely one of erosion. The 

 breccia itself is of very modern age, probably of Quaternary date, and 

 the wearing-out of this great groove must have been an exceedingly 

 modern event. So far as can be seen from the summit of the mountains 

 on either side, no divide can be observed. The erosion seems to have 

 produced a gentle slope on either side of the watershed. At the simi- 

 mit, not over ten miles from the junction of the Atlantic Creek with the 

 Upper Yellowstone, the elevation, 8,081 feet, is not more than 150 feet 

 above the valley of the main stream. The valley is at first quite narrow; 

 but it gradually expands into an open, grassy meadow, which, near the 

 pass, becomes one-third of a mile in width, and gradually closes up again 

 into a caiion on the Pacific slope. So obscure is the drainage that we 

 camped the night of October 3, 1878, within a fourth, of a mile of the 

 water-divide, but did not perceive it until we commenced oiu? march the 

 following morning. 



The conditions are as follows : The summit of the pass for a distance 

 of about half a mile is so nearly level that a marsh is formed, which, in 

 times of high water, becomes a small lake. A portion of the waters 

 from the surrounding mountains accumulates in the marshy meadows, 

 and gradually gravitates from either side into two small streams, one of 

 which flows to the northeast, the other toward the southwest. On the east 

 side of the divide there is a depression or gorge in the mountain, which 

 is occupied by a small stream that at the time of our \4sit flowed in a well 

 marked channel toward the northeast into Atlantic Creek. This is the 

 well-known Two-Ocean Creek. At the base of the mountain-side (c), a 

 small stream rises from a sink-hole, or spring, which at the time the 

 writer saw it (October 4) was nearly dry, and but little water was run- 

 ning in Two-Ocean Creek (a). This spring-hole was not sei)arated from 

 the latter creek more than six feet, and a small dry channel connecting 

 it with a showed that in times of high water a i)ortion of the water that 



