the authors of this paper decided to return to the Park to test 
their conclusions. Thanks to the transportation facilities 
placed at our disposal by Mr. William Nichols, and the kind- 
ness of Miss Adelaide Nichols in driving- us against the traffic 
from Mammoth Hot Springs to Roosevelt Lodge, we were 
able to examine certain of the lavas and to prove conclusively 
that they had flowed up the preglacial valley of the Yellow- 
stone, and had probably served as the dam which impounded 
the water in the canyon. This evidence became increasingly 
clear as we approached the junction of the Yellowstone and 
the Lamar, and is beautifully demonstrated between Junction 
Valley and Tower Creek. Upon our return to the east we 
reexamined the bibliography on the geology 7 of the Yellowstone 
Park. Since the publication of the Yellowstone Folio in 1905, 
we could not find any record that the facts mentioned above 
had been noticed by any previous observers. Upon referring 
to Hayden’s Survey of the park in the twelfth annual report 
for the year 1878, we were surprised and delighted to find that 
Holmes 1 in his excellent geological description of the northern 
portion of the park gives abundant evidence both written and 
pictorial that he had observed several of the important features 
given in detail later in our paper, and that he was on the verge 
of reaching the same conclusion as we do. We feel that we 
could not do better than to quote the following paragraphs 
from his paper : 
“Something of the past history of this Valley can be learned 
from the facts here observed (at Jasper Creek, now shown on the 
map as Deep Creek). A stream — whether the Yellowstone or 
not, no one can say with certainty — had cut down through the 
Tertiary strata to a depth of 600 feet below the top of the present 
valley, and about 400 feet above the bed of the present river. 
The lava has flowed into it, filling the valley to the depth of 200 
feet or more. Whether this occurred before or after the flow of 
the rhyolite I am unable to say from any facts observed, although 
on general principles we would probably be safe in concluding 
that it is more recent. The debris at the ends and on the top of 
the mass of basalt make it difficult to say whether it passes 
beneath the rhyolite of the main wall of the canyon or is simply 
set against it. The fact that it does not continue across the crater 
to the right, as seen in the drawing (plate 21, p. 38), proves 
nothing, as the rhyolite, which extends down the opposite spur to 
a point considerably below the base of the basalt, may have been 
1 U. S. Geol. and Geogr. Surv. of the Territories of Wyoming and Idaho, 
1878, Part II, pp. 39-40. 
Am. Jour. Sc. — Fifth Series, Vol. XVII, No. 99, March, 1929, 
