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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Creek in size and general features. There are relatively deep pools in each of these 
forks, particularly in the lower parts. 
We seined all of these creeks quite carefully and found plenty of small trout every- 
where on each side. We took specimens in each arm of each of the Y’s of Atlantic 
Creek and in such places as would have easily permitted them to pass from one side to 
the other, and there is no doubt whatever that trout can and do pass over this divide 
at will. 
As is well known, Yellowstone Lake is abundantly supplied with trout, while 
Shoshone and Lewis lakes, two very similar bodies of water, were wholly without any 
lisli life. The absence of fish from Shoshone and Lewis lakes is readily explained 
by the presence of vertical falls in Lewis River. But the much greater falls in the 
Lower Yellowstone River would certainly prove as effective a barrier in preventing fish 
from ascending to Yellowstone Lake from the Missouri. Evidently, Yellowstone Lake 
and the Upper Yellowstone River were stocked from the west, and almost certainly via 
Two-Ocean Pass. The probability that the outlet of Yellowstone Lake at one time 
was toward the Pacific, as claimed by geologists, only strengthens this solution of the 
problem. But while this explains the origin of the trout of Yellowstone Lake, it leaves 
another equally interesting problem without any explanation, viz, the presence of the 
blob ( Cottus bairdi punctulatus) in Pacific Creek and its absence from Atlantic Creek 
and the entire basin of Yellowstone Lake. 
We caught four blobs in Pacific Creek in the pass, but though we seined carefully 
in Atlantic Creek, only a few yards away, we did not find a single blob ; nor were we 
able to find any further down Atlantic Creek or in any of the streams tributary to 
Yellowstone Lake. This fish could surely get across just as easily as the trout, and 
the four we caught would have had to travel upstream but a few rods through a 
channel filled with an abundance of water in order to be on the Atlantic side. 
The water of Atlantic Creek and the Upper Yellowstone River does not seem 
to differ in any way from that of Pacific Creek, and the conditions there seem just as 
favorable to blobs. At present I am wholly unable to account for their absence; the 
matter needs further investigation. 
During the night that we camped in Two-Ocean Pass (August 17-18), ice froze 
half an inch thick in a basin at our camp, and nearly as thick on the creek near by. 
The temperature of the air at 6:30 a. m. was 33°; of the water at 8 a. m., 42°; at 11 
a. in., 55°. According to the U. S. Geological Survey, the elevation of Two-Ocean 
Pass above sea level is about 8,200 feet. 
The “Lake sheet” of the map of the Yellowstone National Park by the U. S. 
Geological Survey includes Two-Ocean Pass, but it needs changing in some particulars. 
All of the line representing Pacific Creek above the pass should represent the South 
Fork of Atlantic Creek, and should be connected with the North Fork at the east 
edge of the pass ; and Pacific Creek should be made to come into the pass from the 
northwest. (See diagram, Fig. 3, PI. ii.) 
