142 B. N. A. BOUNDARY COMMISSION. 
346. With this division Dr. Hector correlates group ©, of his general 
section, composed of dark clays, with septarian nodules. These beds, 
however, I have, I believe, clearly identified as forming an integral part 
of Meek and Hayden’s 4th group, as displayed in the vicinity of the 
Line, a conclusion also warranted by the fossils obtained by Dr. Hector 
in them. If this is the case, none of the beds described by Dr. Hector 
can be cited as representing No. 3, unless, indeed, a part of those 
included under D., may belong here. The rocks which appear to come 
up from below No. 4, near the East Fork of Milk River, already fully 
described ; (§ 280) from their position might represent the Niobrara 
group, and it is worthy of remark, that in their lithological character 
they pretty closely resemble Dr. Hector’s group D. Limestone beds, or 
even rocks containing many calcareous fossils, are, however, altogether 
wanting, and the occurrence of richly carbonaceous clays so close below 
the base of Ne. 4, is somewhat anomalous. A similarity also suggests 
itself between these beds and those described by Dr. Hayden, * 
as directly underlying the Judith River fresh and brackish-water de- 
posits. These Dr. Hayden provisionally classes with Cretaceous No. 1, 
and has observed in another locality, to pass beneath No. 4; which 
appears to prove that in this particular region, Nos. 2 & 3, are unrepre- 
sented. The lithological resemblance is moderately close. 
Cretaceous No. 4. Fort Pierre Group. 
347. This group appears to occupy a very great extent of country in 
the region north of the forty-ninth parallel The junction of this part of 
the formation with that next below it, is pretty definite, and there is 
not the same palontological and lithological blending, that occurs be- 
tween the three members below it. At its base, occurs the first real break 
in the typical Cretaceous series of the interior of the continent; and 
here the line separating the upper and lowey portions of the Cretaceous 
has been placed. In the Nebraska section, this division is represented 
by a great thickness of “ fine, grey, and dark-coloured clays, in moderately 
distinct layers, but never presenting a laminated or slaty structure, like 
the Fort Benton group. When wet the clays are soft and plastic, but on 
drying they often crack and crumble so as to obliterate the marks of 
deposition in vertical exposures.”+ Toward the base, there occurs in this 
division, in some places, a local bed of from ten to thirty feet in thick- 

_ _* Proc. Acad, Nat. Sci. Phil., May, 1875. 
t Geological Report Yellowstone and Missouri Expedition, p. 19, 


