308 Barriers to Dispersion of River Fishes 



out from it. Running back among the mountains to the north- 

 ward are two small canyons down which come two small streams. 

 On the opposite is another canyon down which comes another 

 small stream. The extreme length of the meadow from east 

 to west is about a mile, while the width from north to south 

 is not much less. The larger of the streams coming in from 

 the north is Pacific Creek, which, after winding along the western 

 side of the meadow, turns abruptly westward, leaving the meadow 

 through a narrow gorge. Receiving numerous small affluents, 

 Pacific Creek soon becomes a good-sized stream, which finally 

 unites with Buffalo Creek a few miles above where the latter 

 stream fiows into Snake River. 



' ' Atlantic Creek was found to have two forks entering the 

 pass. At the north end of the meadow is a small wooded canyon 

 down which flows the North Folk. This stream hugs the bor- 

 der of the flat very closely. The South Fork comes down the 

 canyon on the south side, skirting the brow of the hill a little 

 less closely than does the North Fork. The two, coming to- 

 gether near the middle of the eastern border of the meadow, 

 form Atlantic Creek, which after a course of a few miles flows 

 into the Upper Yellowstone. But the remarkable phenomena 

 exhibited here remain to be described. 



"Each fork of Atlantic Creek, just after entering the 

 meadow, divides as if to flow around an island, but the stream 

 toward the meadow, instead of returning to the portion from 

 which it had parted, continues its westerly course across the 

 meadow. Just before reaching the western border the two 

 streams unite and then pour their combined waters into Pacific 

 Creek; thus are Atlantic and Pacific creeks united and a con- 

 tinuous waterway from the Columbia via Two-Ocean Pass to 

 the Gulf of Mexico is established. 



"Pacific Creek is a stream of good size long before it enters 

 the pass, and its course through the meadow is in a definite 

 channel, but not so with Atlantic Creek. The west bank of 

 each fork is low and the stream is liable to break through any- 

 where and thus send part of its water across to Pacific Creek. 

 It is probably true that one or two branches always connect 

 the two creeks under ordinary conditions, and that following 

 lieavy rains or when the snows are melting, a much greater 



