PROCEEDINGS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. cli 
geology, and he advised his students, if they ever had an opportunity 
of doing so, to visit the region for themselves. Twenty-two years 
later, namely, in the spring of 1902, having occasion to be in 
America, I remembered and followed his advice, and found that his 
description, instead of being exaggerated, failed to give an adequate 
idea of the reality. Indeed, no verbal description can convey a true 
impression of this wonderful region. 
The River Colorado, with its tributaries, the Grand and the 
Green Rivers, drains the great plateau region of Western America 
lying between the Rocky Mountains and the Wahsatch Mountains. 
This region occupies an area of 240,000 square miles, and embraces 
the greater portion of the States of Wyoming, Utah, Colorado, 
Arizona, and New Mexico. It drains into the Pacific Ocean, at the 
northern extremity of the Gulf of California. It derives its name of 
Colorado (Spanish, “Red”) from the prevailing colour of the rocks 
through which it flows. The most remarkable portion of its course, 
however, is found in the last 250 miles, where it cuts through the 
great Colorado Plateau, in the State of Arizona. This plateau con¬ 
sists of an arid table-land, elevated some 7000 feet above sea-level, 
and built up of nearly horizontal strata of Sedimentary rocks. 
Through this mass of level strata the river has, through the course of 
long ages, cut its way to a depth of about 6000 feet, forming a gorge, 
or rather a succession of gorges, whose sides rise in a series of cliffs 
and terraces. Owing to the dryness of the climate these walls of the 
Canon do not get bevelled off in slopes of easy gradient, as do the 
sides of valleys in a more humid climate. The result, from a scenic 
point of view, as can easily be imagined, is grand in the extreme. In 
some places stupendous walls of rock rise sheer up to the height of 
1000 or 1500 feet, while in other places they get broken up into 
pinnacles and spires and domes of every conceivable shape. One of 
the most striking features of the scene is the variety of colouring of 
the rocks, which extends through every gradation of red, purple, 
yellow, and orange, and from black to white. The formations 
exposed in this gigantic geological section extend from the primeval 
Gneiss at the bottom of the cleft right up through all the Palaeozoic 
rocks, as far as the Permian formation. The interest of the scene to 
a geologist is twofold, for, in no other region can the effects of 
denudation be seen on such a gigantic scale, and in no other spot 
can so many of the geological formations be seen exposed in one 
section. 
Sir Archibald Geikie, in his Text Book of Geology, gives the 
thickness of the various strata represented in the Canon as follows :— 
Thickness. 
Permo-Carboniferous. 
8. Bellerophon Beds, 
( 7. Cherty Limestone, - 
| 6. Cross-bedded Sandstone, - 
250 feet. 
350 „ 
Coal-measures. 
200 ,, 
(5. Aubray Red Shales, &c., - 
1200 ,, 
Lower Carboniferous. - 
I 4. Red Wall, 
^ 3. Tonto Group, - 
' 2500 „ ’ 
300 ,, 
2. Silurian Rocks, 
300 ,, 
1. Granite, Schist, &c., 
1200 ,, 
Total, 
* 63OO „ 
o 
