62 GEOLOGY. 
The theory of the origin and mode of formation of the valley of the Little Colorado has 
seemed to me to be quite simple, and has been already adverted to. It has evidently been 
the channel through which the drainage of the northern slopes of the Mogollon and San Fran- 
cisco mountains found its way to the Colorado since the dawn of the present geological epoch. 
This flow of water has washed off the variegated marls and red sandstones which, to the depth 
of more than two thousand feet, once covered the Carboniferous limestone, and the broad 
valley is the legitimate consequence of the action of such an agent on such materials. When, 
however, the harder substrata had been reached, and at the same time the precipitation of 
moisture was, for the most part, restricted to the mountains, the eroding force of the drainage 
of all that country was expended in deepening the narrow beds of the water-courses. Through 
countless ages this process has continued until the remarkable results I have described have 
been effected. What was once a broad and fertile valley, abundantly watered by the streams 
meandering through it, by the simple process of the deepening of the beds of these streams, 
and hence its more perfect drainage, has been converted into an arid and sterile plain, ren- 
dered absolutely impassable hy the profound chasms which cut it in every direction. 
CANON OF CASCADE RIVER. 
In attempting to reach the junction of the Great and Little Colorados we descended to the 
plain to which I have referred; entered and traversed for some miles a cafion leading in the 
right direction. This proved to be but a tributary to the greater caiion of Cascade river, in 
which the progress of our party was arrested by cascades. 
In the strata exposed in the walls of these cafions I found a continuation of the geological 
column to the top of the Carboniferous series. This section is connected with that of Diamond 
river by the Mountain (?) limestone, which forms the summit of the first and the base of the 
last. The members of the Carboniferous formation are here all fully exposed; their intimate 
characters, their thickness, and the order of super-position being as readily determinable as 
are those of the older paleozoic rocks on Diamond river. 
The section here displayed is composed of the following constituents: 
Section in caiion of Cascade river. 
1, Limestone, varigated, crimson and lemon-yellow, with nodules of chert and 
WM UP OOD Gr MG Sore oe ee decay Cee PERSE) OPO S 50 feet. 
2. Sandstone, coarse, drab, sometimes pinkish; in places containing many small 
quartz pebbles and imperfect vegetable impressions..--.- +... ...2.2eseees BE ee 
3. Massive cream-colored limestone with geodes, containing calc. spar-.-......-- iS Bee 
4 wisn victhattie tulehdettadrela gc ant ik ce EK gk ML EAKI EES ee Oe reer ee ae 
5 Cherty Hitiobtond So Cie DOA ee OI ho BORE Dee Ge epee ter yd 
6. Blue limestone, with Productus semireticulatus, etc., very abundant----.-..--.. oe 
1. Cherty limestone, light-blue, containing Productus semireticulatus, P. occi- 
dentalis, (n. sp.,) Spirigera subtilita, Orthisina umbraculum, Rhynconella uta, etc. 175“ 
8. Shales, green, red, and white, with Snowy gypsum: .-..+......... oe cee wee ie 
9. Hard blue limestone, containing crinoidal columns—spines of Archeocidaris, 
Producti, irigert pe eos Ce eee eee Se ee ee 100 ff 
10. Soft lemon-yellow limestone, with few Productus WA ern ca os bane 5 90.34 
11. Drab, cross-stratified sandst “ONE pg eerny ma UB eee 
12. Red calcareous sandstones and shales, with SYPSUM------ 2 ee eee eee 350 * 
