266 TERENCE T: QUIRKE 
Total thickness about 400 feet. 
Most of the rocks are water laid, but part of member No. 3 is 
Eolian. The rocks are characteristically loosely cemented and very 
friable, but some of the sand is indurated to quartzite. The cement 
is chalcedonic and opaline quartz. Many pieces of opal were 
found; some are transparent and very pale blue, others are milky 
white, and a few are dark brown with white streaks resembling the 
grained appearance of silicified wood. 
The limestone layers are all siliceous, the silica being in very 
fine grains. Some of the limestone is clearly clastic in character, 
the constituent grains being distinguishable by the naked eye. 
One specimen of limestone taken from the upper hard layer con- 
tains 47.7 per cent CaCO,, but the sand content lowers the amount 
of CaCO, below this figure in most of the rock. 
The clays are characteristically pale green or pink, loosely 
granular in texture, and but slightly plastic. When a piece of the 
green clay is dropped into water it falls into fragments. Within a 
minute after a small piece is put into water it has disintegrated into 
very small flakes which have the appearance of a green, flocculent 
precipitate. When made into stiff mud and used as a plaster the 
clay hardens on drying and serves the people of the district in place 
of lime. Although they call it “‘natural lime” and use it for many 
purposes, even in place of putty to fasten glass in window sash, as 
mortar, and as a wall wash, the rock contains less than 2 per cent 
lime. 
Correlation with White River deposits.—These rocks are uncon- 
formable on the Fort Union formation. The only sedimentary 
beds which are known to lie on the Fort Union formation in North 
Dakota belong to the White River formation. These beds are 
White Butte, Little Badlands, and Sentinel Butte deposits, all of 
which are similar to the Killdeer beds. White Butte deposits near 
Sandcreek post-office, Billings County, were discovered by Cope 
in 1883. He wrote: ‘The beds, which are unmistakably of the 
White River formation, consist of greenish sandstone and sand 
beds of a combined thickness of about too feet. These rest on 
white calcareous clay rocks and marls of a total thickness of too 
feet. These probably belong to the White River epoch, but con- 
