536 A. C. PEALE 
Montana group, or Fort Pierre and Fox Hills formations. He was especially 
impressed by the occurrence, in the upper part of these underlying beds, of a 
zone containing Cardium speciosum, Mactra alta, Tancredia americana, and 
other forms which in north-central Colorado are known to occur only in the 
Fox Hills beds immediately beneath the Laramie. No beds higher than the 
Judith River were seen, and the view was adopted that the Judith River series 
overlies all of the Montana group and is referable to the Laramie. When a 
few days later the overlying marine Cretaceous shales were seen in contact 
with upturned Judith River beds near Havre, Mont., their apparent position 
was supposed to be due to faulting, of which there was abundant evidence in 
the neighborhood.! 
As a result of this work Dr. Stanton? gave Mr. Whitman Cross 
the following section made in Dog Creek, published in 1896: 
The fresh-water Judith River beds are well exposed in bluffs on Dog 
Creek, 4 or 5 miles from the mouth of Judith River, and also on the north side 
of the Missouri within 3 or 4 miles of the same place. The section in this 
neighborhood shows about 650 feet of marine Cretaceous strata overlain by 
300 to 350 feet of fresh-water beds. The succession of strata and thickness as 
estimated by Mr. W. H. Weed are as follows, beginning at the base: 
1. Soft, dark clay shales. 
2. Band of ferruginous sandstone with Avicula linguiformis, Inocera- 
mus cripsii, Baroda wyomingensis, Placenticeras placenta, etc. 
. Shales like No. 1. 
3 
4. Coarse gray laminated sandstone. 
5. Carbonaceous shales with bed of lignite at base............ 100 
6. Brown sandstone with great numbers of Cardium speciosum 
andua ste wrOther: SMe CleSe) sere. vere) ace in tegen ate ct ect pekaee eae 30 
a Sandly; Shales vane Geant che ccge., ees oir nah a) co mae eae 25 
8. Dark clay shales with concretions containing Baculites ov atus in 
lower portion and sandy bands and concretions near the top witha 
characteristic Fox Hills fauna including: 
Nucula sp. Liopistha (Cymella) undata 
Clisocolus cordatus Pholadomya subventricosa 
Callista nebrascensis Mactra formosa 
Tellina aequilateralis Lunatia subcrassa 
Tancredia americana Baculites ovatus 
The total thickness of this bed was not seen at any one place, but it is at 
least: 350 feet. 
Immediately above these dark shales is a bed of greenish-yellow sandstone 
which occasionally forms bluff exposures 50 or 60 feet high, but usually only 
slightly exposed in steep slopes and largely covered by wash from the softer 
and lighter-colored beds above. This was taken as the dividing line between 
«Stanton and Hatcher, Bull. U.S. Geol. Surv., No. 257, 1905, p. 10. 
2 Monographs U.S. Geol. Surv., XXVII (1896), 239-41. 
