DESCRIPTIVE GEOLOGY. 15 
200 feet or more. A similar coloring of both the granite and the 
gneiss was noted in Black and Boulder canyons and in several places 
south of Williams River. 
Metamorphosed sediments, consisting of quartzites, argillites, and 
limestones, occur in several localities in northwestern Arizona. These 
were observed in Virgin Canyon at the northern end of the region, in 
Williams Canyon, and in the Granite Wash Hills in the vicinity of 
Harrisburg. They are highly metamorphosed, faulted, tilted, and 
more or less included as blocks within the granites and gneisses. They 
were nowhere observed in contact with the Cambrian, but on account 
of their high degree of metamorphism and their intimate association 
witli granites which, in the cliffs region, lie beneath the Cambrian 
sandstone, are here regarded as probably pre-Cambrian rocks. 
CAMBRIAN. 
According to the various writers who have described the Grand 
Canyon region, Cambrian rocks occur in Grand Canyon and are 
identical in character with those in the cliffs in the eastern part of the 
area described. They consist of a coarse-grained basal quartzite 80 
to 100 feet thick, overlain by about 600 feet of }^ello wish-green 
arenaceous shale. The quartzite and shale together comprise the 
greater part of the Tonto formation of the Grand Canyon section. 
CARBONIFEROUS. 
Resting with apparent conformity upon the Tonto formation is the 
Redwall limestone (the Devonian of Grand Canyon described by 
Walcott a was not identified in the cliffs), which is 1,000 feet or more 
in thickness where examined. 6 From Music Mountain southward 
this limestone is separated more or less distinctly into an upper and 
a lower division. The upper part is massive, with little tendency 
toward separation into layers even in weathered surfaces. The 
lower part, although consisting mainly of limestone, is made up of 
distinct layers, often separated by thin seams of clay. 
In Truxton Canyon two small collections of fossils were obtained 
from the Redwall limestone. These were examined by G. H. Girty, 
of the Geological Survey, who reports the following lists. 
At Yampai, near the top of the exposed section, the following were 
obtained : 
Derbya? sp. 
Composiia a IT. C. suhtilita. 
Aviculipecten sp. 
A \ iculipecteii sp. 
Aviculipecten sp. 
Myalina sp. aff M. meliniformis and M. 
congeneris. 
Edmondia? sp. 
" Walcott, C I)., Am. .lour. Sri., 3d ser., vol. 20, 1880, pp. 22] 225. 
'Mi. K. Gilbert's section a1 the mouth of Grand Canyon shows ;i thickness of 2,675 feel in the Redwi 
limestone. 
