134 RECONNAISSANCE FROM CARROLL, MONTANA, 
interval on both sides was small, aud we should regard an estimate of 100 feet for the total thick- 
ness as a largeone. Inregard to this, Dr. Hayden says: “The Jurassic rocks are crushed together 
in the uplift to such an extent that they are quite obscure, and do not appear to much advantage ; 
but, in Union and Flathead Passes, they are much better exposed.” Lis final estimate of their thick- 
ness is not clearly stated; but elsewhere, in the same vicinity, he speaks of them as 1,200 feet thick. 
Whatever may be the facts at this point, we can safely affirm that the development of Jurassic 
rocks to the north and east is very limited. We had several opportunities for examining beds pos- 
sibly Jurassic, in search of fossils; but in no case were we successful in our efforts to find such 
remains. On the contrary, in two distinct localities we passed from undoubted Cretaceous to 
undoubted Carboniferous, with a very small interval between of non-fossil-bearing strata. These 
intervening strata may very possibly belong to Jurassic time, and their apparent absence elsewhere 
may be due to the disturbing influences of the uplifts; but their relative insignificance seems to us 
quite certain. Banks of red soil were conspicuous at several points, and in appearance suggested, 
to a certain extent, the “ Red Beds” referred to the Triassic in other localities. Iu three distinct 
cases, however, we found such layers immediately underlaid by Cretaceous sandstones; so that we 
think that the beds in question must belong in all cases to the latter horizon. 
Cretaceous.—To the Cretaceous formation belongs the rock underlying the prairie over nearly 
all of the route traversed by us. We were unable, however, to obtain any satisfactory results as to the 
succession of the various beds. ‘The sandstones, of which these rocks for the most part consist, are 
quite different at the various localities at which they were seen. They are generally without fossils, 
though frequently containing indistinet vegetable remains, and seem to lack any particularly dis- 
tinctive or characteristic features. They have been so often described in the preceding pages that 
it is needless here to enlarge upon them. The lower part of the formation must be that visible on 
the Bridger Mountains, directly overlying the Jurassic. Very little is in sight, however, and the 
fossils obtained were very poor. When the rocks appear agaiu in the valley, they are mostly the 
constantly-recarring “ somber” sandstones. At®the headwaters of Cottonwood Creek (see p. 122), 
we obtained a few poor fossils in a bed which stratigraphically was the lowest in a series of 5,000 
feet involved in a gigantic fold. One of these fossils is credited to Cretaceous No. 2 of Meek and 
Hayden. From here up, in the order of their time, the rocks have been briefly mentioned. They 
are mostly dark-colored sandstoues, occasionally shales, aud all nearly destitute of remains of life. 
The only suggestions of fossils are the indistinct vegetable remains before mentioned, which were 
found best preserved in the upper strata. The thickness of this Cretaceous series has been esti- 
mated at 5,000 feet. Most of it is referred by Hayden, though without facts, to the doubtfal “ Coal 
Group, forming the transition from the Cretaceous to the Tertiary”. We regard them all as properly 
Cretaceous; in fact, in some of the upper strata, fossils belonging to No. 5 were found. As has 
already been stated, beds of red clay immediately overlie some of the lowest Cretaceous strata ; 
and, though their character is probably local and changeable, they are so noticeable where they 
occur that they deserve mention bere. 
Cretaceous No. 4.—The most distinctly-marked and characteristic member of the Cretaceous is 
No. 4, or the Fort Pierre clays, which have already been fully described. Their thickness was esti- 
mated at 700 to 1,000 feet. They extend from Carroll north and south for a distance of twenty-five 
miles from the Missouri. Further than this, they were observed below on the river one hundred 
and fifty miles from Carroll, and from here to the Judith River a distance of two hundred miles. 
Beds referred to these take part in the uplifted strata, both at the Judith Mountains and the Little 
Rocky Mountains, overlaid by Cretaceous No. 5. The Fort Pierre clays were not observed at any 
greater distance from the river than the points mentioned ; aud this is true, although beds both 
below and above them have shared in the folding near the Bridger Mountains. From this, it is con- 
cluded that the Fort Pierre clays are limited to the immediate valley of the Missouri at this point, 
In other words, while the conditions were such as to cause an immense accumulation of mud in what 
s now the immediate valley of the Missouri, different conditions prevailed at a greater distance 
from the river, and deposits of sandstone were going on. 
Cretaceous No. 5.—The Fox Hills Group was determined beyond all question at three points: 
at Box Elder Creek, near the Judith Mountains; at Haymaker’s Creek, near the Forks of the Mus- 
selshell; and at the mouth of the Judith River. The rock in each case was a sandstone, which is 
