216 
THE GEAND CANON DISTEICT. 
the waters became fresh, and remained so until they disappeared altogether. 
This change was not limited to the Plateau Country, hut appears to have 
been general over the greater part of the western mountain region. In 
truth, I know of no more impressive and surprising fact in western geology 
than the well- attested observation that most of that area has been covered 
by fresh-water lakes, and that the passage from the marine to the terres- 
trial condition seems to have been through an intermediate lacustrine con- 
dition. The marvel is not in the fact that here and there we find the ves- 
tiges of a great lake, but that we find those vestiges everywhere. The 
whole region, with the exception of the mountain platforms and pre-exist- 
ing mainlands, has passed through this lacustrine stage. 
When we take account of the peculiar circumstances our surprise may 
diminish in some measure, and the facts thus described may seem natural 
enough. The uplifting of the western region was a movement which acted 
unequally over the continent. Some portions were raised more than others. 
It is also to be considered that some of the inequalities of the surface ex- 
isted before this general uplifting began. The result of this inequality must 
necessarily have been the production of depressed basins and intervening 
watersheds. Whether these basins would be completely closed, so as to 
form great lakes, or whether they should have drainage freely to the ocean, 
would depend of course upon the relations of the new axes of displacement 
to the older topography. If the new displacements merely accent and in- 
crease the older features, we should hardly look for the formation of lake 
basins. But if the new displacements are in any marked degree independ- 
ent of the old ones, and if their axes lie transverse or oblique to the older 
axes, the formation of lake-basins in a newly emerging country is inevita- 
ble ; and if the area affected be very extensive the chances are that the 
basins will be either very large or very numerous — in any event covering 
the greater part of the area. Without speculating as to the cause, it may 
lie laid down as a general fact that the broader displacements of the West 
which began in early Tertiary time are quite independent of the older 
topographies, and the production of lake-basins by the new emergence 
seems a necessary consequence. 
It is apparent in any event that the Plateau Country formed one con- 
