FIO RECONNAISSANCE FROM CARROLL, MONTANA, 
where they are followed by about 5 feet of a firm limestone, and that by a considerable thickness 
of green and black shales, which last may be traced for a short distance on both sides of the stream. 
It is to be noticed that the strike and hence the dip of similar layers on both sides of the stream is 
quite different; and, though further study is needed to make out all the facts, we think it can hardly 
be doubted that at this western end of the mountains there is a distinct fold; the axis probably 
running a little north of west. 
Continuing up to the source of the stream, we found the limestone here with a very slight dip 
to the northwest; strike northeast. The final point which we reached was a little caiion, with high 
and bold limestone walls, from which we obtained a few not very perfect Carboniferous fossils, viz: 
1. Zaphrentis centralis (2), Ev. & Shum. 
2. Streptorhynchus Keokuk, H. 
3. Spirifera centronata, Winch. 
4. Stictopora, sp. 
To reach these Carboniferous rocks, we had doubtless passed over in succession the Cretaceous 
rocks, having perhaps a thickness of 900 feet, and also the Jurassic, if it exists here. We found no 
fossils belonging to this age, and doubt the existence of any considerable thickness of Jurassic beds. 
The limestone with the green and black shales noted above may possibly belong here. 
Leaving the ridge, we turned at right angles to it; that is, nearly north. Here we passed over, 
first, the limestone dipping northwest, then successive beds of sandstone with beds of red clay inter- 
stratified. Near the foot of the hill, a reversal of the dip occurs in the sandstones, pointing toa 
minor fold parallel to the general course of the range. No older rocks than the Carboniferous lime- 
stone were observed ; and from the numerous limestone pebbles containing Carboniferous fossils, 
picked up at different points along the sides of the mountains, it is safe to conclude that the range, 
as a whole, is made up of Carboniferous limestone; the younger rocks lying on its outer slopes. No 
evidence of any older rocks than the Carboniferous was noted ; certainly not of any crystalline rocks. 
The trachyte, so common in the neighboring Judith Mountains, seems to be almost or entirely 
absent, 
LITTLE BELT MOUNTAINS. 
The Judith Gap is the divide between the Judith and the Musselshell Rivers. At this point 
the Little Belt Mountains and the Snow Mountains approach one another quite closely. The 
former are quite an extended and somewhat irregular range, reaching for a long distance north and 
west. Of its general geology, we can say little, as we can speak only of a few widely-separated 
points where we were able to visit it. One of these points was the extremity of the range at the 
Judith Gap. Near the Gap, we have already spoken of finding, on the north side, beds of red 
clay, which are associated with a little limestone, and nearer the hills with an underlying sandstone. 
Crossing the hills, which form the extreme eastern end of the range, perhaps a mile west of the Gap, 
we found a bed of yellow sandstone, which contained Ostrea congesta, Con.; then, some distance up 
the slope, a limestone containing corals, and dipping in a northerly direction; then some thin layers 
of limestone containing Productus. 
The fossils found here were as follows; the identification by Mr. Whitfield: 
. Ostrea congesta, Con. 
. Cyathophylloid coral. 
. Campophyllum torquium, Owen ??. 
. Spirifera centronata, Winch. 
. Spirifera, sp. May possibly be Spiri/erina Wentuckensis. 
. Productus, sp. Resembles P. Wortheni, I.; but perhaps more nearly related to P. multi- 
striata, Meek. 
7. Schizodus, sp. Nearly or quite 8. Rossicus, (DeVern.,) M. & W. 
Here were seen. 20 feet of green and black shales, dipping 50° northeast. From here, as we 
go up and across the hills, the strike gradually changes, and with it the dip, so that on the south 
side of the hill we have strata dipping southeast instead of northeast. ‘The succession observed 
here is ‘from below up: 
Limestone, dip 65° south, strike north 70° east..............cceeee econ sees 2 feet. 
Red clays, with purple slates underlying it.....2.. 20... eee eee eee eee 10 feet. 
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