146 The American Geologist. 
March, 19f)5 
prominent they are very black in color. Iron is a constant im- 
purity, and brown or yellow staining of surfaces and veinlets or 
fissures following water seepage, is a noticeable effect. 
Thickness 300 f eet+ 
D. A series of 10 alternating black and white bands, the thickest 
being about 6 inches. The black bands are carbonaceous while 
the white ones are siliceous but not gritty and have a decided 
alum taste. The contrast between these two types is very strik- 
ing and theirj)ersistence throughout the Pembina mountain dis- 
trict makes them a good datum horizon. 
Thickness G feet. 
C. A bed of dark shale heavily stained with ii'on and carrying 
locally excessive quantities of gypsum. Lies just below the 
black and white series and in places its firmness causes a shelf- 
like break in the bluffs where this bed is exposed. 
Thickness 4 feet. 
B. Yellowish or bluish-gray massive limy shales or marls, carrying 
20-70 per cent calcium carbonate in their composition. They 
are not uniform throughout their whole thickness, but are re- 
solvable into a series of beds depending upon the lime content 
for their distinction. They are more massive and block-like in 
their habit and more uniform in their appearance than any other 
beds of this area. They are locally called "cement beds." 
Thickness 150 feet + 
A. Greenish and grayish black laminated shales weathering into 
plastic clays. They are low in lime to a limit of less than one 
per cent. The change from the n"xt overlying beds to this is 
gradual and is marked by the change to low lime content. No 
sharp line can be drawn. There are occasional horizons of con- 
cretions, septcrian nodules and gypsum crystals. 
Thickness 250 feet.+ 
The above series of beds forming the Pembina moun- 
tains are supposed to correspond to the different sub- 
divisions of the Cretaceous recognized by Babcock* as fol- 
lows : 
E. — 300 ft. black and gray shales. — Pierre. 
D. — 6 ft. black and white bands. 
C. — 4 ft. iron and gypsum bed. 
B. — 150 ft. blue and yellow marls. — Niobrara. 
A. — 250 ft. greenish and black clay shales. — Benton. 
Fossils are rare in these shales. A few traces are seen 
in the Pierre (E) but none were identified. None at all were 
in either D or C. 
• But in B, and in the talus clays and marls along the 
*First Bieuiital Report, Geological Surrey of North Dakota, 1S91, E. J. Babcock- 
pp. 18-23. 
