THE GRAND CANYON OF THE COLORADO. 319 
Cambrian sandstone. The former were planed off to a baselevel 
before the deposition of the latter. 
CHUAR TERRANE. S 
The first division of the Chuar terrane is from the summit 
of Nunkoweap Butte, on the divide between Nunkoweap and 
Kwagunt Valleys, down the south side of the butte to the base 
of a massive belt of reddish-brown sandstone. The latter stratum 
was traced to Chuar Valley, where it caps the lower division of 
the terrane on the north side of the valley. The lower division 
terminates in argillaceous shales resting on a massive magnesian 
limestone south of Chuar Brook. 
Section from the Summit downward. 
UPPER DIVISION. 
1. a. Massive reddish-brown sandstone, with irregular ‘layers 
of similar color and containing numerous fragments of 
sandstone-shale of lighter color - - - 2 25 
6. The sandstones of 1 become shaly near their base and 
pass into a reddish, sandy, and then argillaceous shale, 
with a few thin, compact layers of sandstone in the shale 75 200 
2. Black, fissile, argillaceous shale, that crumbles on exposure 
to the weather - - - - - - 225 
3. Compact gray limestone in massive layers; buff on 
weathered surface - - - - - - 50 
4. Shale similar to 2 - - - - - 60 
5. Gray limestone similar to 3 - - - - - 50 
6. Black argillaceous shale, similar to 2 and 4 - - 140 
7. Hard buff limestone, with irregular odlitic, cherty bands 
that at times constitute most of the stratum - - 4 
8. a. Black argillaceous shale, with compact layers 2 or 
3 inches thick — - - - - - - 30 
6. Dark, earthy limestone - - - - I 
c. Black shale - - - - - Ai 1D 
aa 33 
g. Gray, Stromatopora* (?) limestone - - - - 8 
10. Black argillaceous shale, with variegated shales below, con- 
taining more or less arenaceous matter in the form of 
arenaceo-argillaceous shale and thin layers of sandstone. 
* Probably a species of Cryptozoon. 
