130 GEOLOGICAL SKETCH OF THE ESTUARY AND FRESH WATER DEPOSIT 
About ten miles below the mouth of the Judith River, the Marine strata of No. 1, are 
seen to rise rapidly from beneath the Estuary and fresh water beds, and on reaching the 
mouth of the Judith we have the following vertical section of No. 1, the Estuary and fresh 
water beds only capping the hills and soon ceasing to appear. 
1.—Yellowish and reddish, rather coarse grained sandstone, becoming deep red on ex- 
posure, containing Inoceramus ventricosus, Mactra alta, Cardium speciosum, dc., &c.—20 to 
25 feet. 
2.—Mixed pure and impure lignite—whole bed containing many crystals of selenite 
and a yellowish substance like sulphur. The masses of lignite when broken, reveal in 
considerable quantities small reddish crystalline fragments of a substance having the taste 
and appearance of rosin.—6 to 8 feet. 
3.—Variable strata of drab clay, and gray sand and sandstone; upper part containing 
large numbers of Ostrea glabra. Near the middle, there are gray or ash-coloured clays, 
with very hard bluish gray granular silicious concretions, containing Hetangia Americana, 
Panopea occidentalis, Mactra formosa, &c.—80 to 100 feet. 
The above section will show very clearly both the lithological and paleontological dif- 
ferences in the two deposits under consideration. It will be seen that the beds represented 
by the last section contain only marine fossils, while the fresh water and estuary beds, 
with one exception, have furnished only terrestrial and fluviatile, with a few estuary shells. 
In regard to the age of the marine strata, it is still impossible to arrive at a positive con- 
clusion. Most of the fossils as yet obtained, have a decided Cretaceous aspect, a species 
of Mactra found here being so closely allied to a species occurring in No. 1 near the mouth 
of Big Sioux, which we think we have proved to be of Cretaceous age, that we can find 
no well marked characters to distinguish them. A species of Baculite is also found in 
these beds, scarcely distinguishable from B. ovatus (Say.) This genus has hitherto been 
considered in the Old World as restricted to the Cretaceous epoch; while, on the other 
hand, the genus Hetangia which occurs in bed 3 of section, has never been found in the 
Old World in formations newer than the Lias. With evidence so conflicting before us, it 
would be premature to give any decided opinion, and we can only wait for the results of 
a second exploration of*this interesting region. As we have already said in a former 
paper,* “ We are inclined to think they hold a position near the base of the Cretaceous sys- 
tem, and are probably on a parallel with the Neocomien of the Old World, though they may 
be older.” That well marked Jurassic beds occur at many places along the eastern base 
of the Rocky Mountains from the Saskatchewan to New Mexico, we have little doubt. 
In regard to the age of the fresh water and estuary deposit, the evidence is even more 
* Proceedings of Academy of Natural Sciences, Pa., Memoir by F. B. Meck and F. V. Hayden, 1857, 125. 
