ei = NEW TRACKS IN NORTH AMERICA. 
twenty-two miles we rise again some 200 feet. At about : 
this point we cross a divide, and commence the real ‘descent 
towards the Rio Gila; or, in other words, we enter the basin of ] 
the Aravaypa. This fot i is soon made manifest by the appear- § 
ance of the cafiada of the Aravaypa asa groove at the bottom 
of the trough between the mountains. From the commence- — 
ment of this cafiada to the point where its walls approximate 
so closely as to form the caion proper the distance is 25°30 
miles, in which interval the total descent is 1,104 feet. 4 
As this great fall does not represent the slope of the trough 
between the mountains, but the gradual deepening of the 
groove in its centre (the cafiada of the Aravaypa), it is easy 0. 
understand how the cliffs or sides of the cafiada become highe r 
and higher as we descend. Sometimes they approach each other, 7 
and form a natural gate or narrow passage for the river bed : 
Sometimes they recede to the distance of two or three miles 
apart. In places they have perpendicular walls. Often the y 
become sloping banks, and being composed of soft, = ; 
material, mostly drift, they are sometimes transformed | by 
erosion into very picturesque objects, resembling forts, castles | 
long lines of earthwork, and the like, which are chiefly 1 ; 
markable for the mathematical regularity of their outlines 
thus giving a very peculiar appearance to the whole count y 
since the traveller is never out of sight of these singular fo ma 
tions; for no sooner is one passed than another appears at 
the next turning of the gorge. At the back rise the black , 
shining walls and the deeply-serrated summits of the vol 
ranges on either side. These gradually approach each 
until the trough itself becomes obliterated, and the wall 
the cafiada in its centre are of necessity merged into 
‘Mountain — At the oes where the mountains seem 
