46 
PROCEEDINGS OF THE ACADEMY OP 
Lake, below Fort Clark, led us subsequently to think the whole of these estuary 
beds, near the Judith, might possibly be only an outlier of Tertiary reposing 
upon deposits of the age of our No. 1. At the same time, in consequence of the 
occurrence in them of remains regarded by Dr. Leidyas analogous io Lepidotus^ 
Iguanodon^ and Megalosaurus^ we stated that "in the midst of evidence of such a 
conflicting nature, it is unsafe to express any very positive opinion respecting 
the age of these formations." 
Since we know that there is a similar group of beds at the base of No. 1, as 
we now understand it, near the Black Hills, containing a mingling of freshwater 
and marine fossils, although we are not sure any of them are specifically identical 
with those found near the Judith, we are inclined to think our first views in re- 
gard to these Judith River formations will prove to be correct, or in other woids, 
the beds from which the saurian remains, described by Dr. Leidy, were obtained, 
will yet prove to be a part of the series we include in No. 1 of the Black Hills 
section. This view receives additional support, too, from the fact that the Judith 
River freshwater or estuary formations were often seen much upheaved and 
distorted, while around the Black Hills the Tertiary deposits appear to lie un- 
disturbed upon the upheaved older rocks, in such a manner as to indicate that 
the last period of disturbance amongst the strata of this region occured af- 
ter the close of the Cretaceous epoch, but previous to the deposition of the Ter- 
tiary. 
The evidence pointing to the conclusion that formations A, B, and C of the 
foregoing section should be regarded as probably Jurassic, is, first, the affinities 
of their organic remains ; and secondly, their stratigraphical position. It is true 
we do not pretend to have recognized in these deposits any genera peculiar to 
the Jura ; but at the same time we have failed to identify amongst these fossils 
any species belonging to genera limited in their range to the Cretaceous sys- 
tem ; while in their specific relations, so far as we have been able to make com- 
parisons, they are nearly ail much more closely allied to Jurassic than Creta- 
ceous forms, if not indeed actually identical with the former in some cases. This 
will, perhaps, be better understood by the following comparisons of some of the 
species described in this paper, from these formations : — ■ 
\st Fentacrinus asteriscus^ n. s. p., from near the lower part of formation C, is 
so nearly like the Liassic P. scalaris, Goldfuss, that it is with some hesitation 
we have regarded it as new. 
2d. Avicula (^Monotis) temcicostaia, n. s. p., ranging from the lower part of the 
bed A to near the base of bed C, is very closely related to M. substriata of Min- 
ster, from the Lias. 
"id. Area {Cuculla^a) inornaia, n. s. p., from the lower part of bed A, is very 
similar to C. Munsteri (Zeiien), also from the Lias. 
Ath. Panopcea {Mi/acites) subelUpticay n. s. p., from the bed C, is similar lo 
the Liassic forms M. Liassensis and M. Alduininus of Quenstedt. 
5th. Ammonites cordiformis, n. s. p., from bed A, is of the same type as the 
Oolitic species A. cordatus (Sowerby). 
<oth. Belmniies densus^ n. s. p., from bed A, is scarcely distinguishable from 
the Oolitic species B. ecceniricus, Blinville, if indeed it is really distinct. 
In addition to the above, there are in the collection from the beds A, B, and 
C, other species we have not yet had time to describe, which closely resemble 
Liassic and Oolitic forms. These facts when viewed in connection with the 
stratio-raphical position of these deposits, below what appear to be lower Cre- 
taceous formations, and as above stated, so far as we yet know, the absence in 
them of well-marked Cretaceous types, are, we think, sufficient reasons for sup- 
posing they probably represent the Jurassic system.-^- 
* On a former occasion we expressed the opinion that Mr. Marcou was mistaken in re- 
gard to the existence of Jurassic rocks in the region of the Black Hills. This opinion 
waLS based upon the fact that one of us had traversed the belt of country he intended to 
color, east of these hills, as Jurassic, and found it occupied by Tertiary and Cretaceonjs 
formations. We also knew his map of this region had been mainly colored theoretically, 
[March, 
