THE PERMIAN TERRACE. 
45 
Mr. Walcott’s conclusion is no doubt the best which can be reached 
with our present knowledge, but it is very inconvenient and awkward to 
the geologist who is required to map the distribution of the strata and their 
topographical features. In all of the other formations each group forms its 
own terrace or series of terraces. As we descend them we find ourselves, 
when we reach the foot of the Eocene cliff, upon the summit of the Cre- 
taceous. Reaching the foot of the Cretaceous cliffs, or slopes, we are upon 
the broad expanse of the Jurassic platform. Descending the Jurassic, we 
find the Trias coming out from the base of the Jurassic Cliffs; but when we 
descend the Vermilion Cliffs, we have not reached the Permian. The Trias 
is still beneath us, pushing out its basal member, the ShinArump conglome- 
rate, clear to the crest-line of the Permian wall. In the Jui’assic terrace 
and in its terminal cliff we find none but Jurassic strata. Similarly, also, 
in the cliffs and terrace platforms of the Cretaceous and Eocene; but the 
Permian terrace is everywhere sheeted over with a solitary stratum of the 
Trias. Somehow we cannot help thinking that the conglomerate has no 
business there, and that it ought to have been cut off at the base of the 
Vermilion Cliffs, or else it ought to be relegated to the Permian. In deline- 
ating the distribution of the formations by means of colors on the map, the 
ordinary practice would require us to extend the Trias to the brink of the 
Permian Cliffs, for in such delineations we only profess to show the surface 
exposures of the several groups; but this would confound the Permian ter- 
race with the Trias, and obliterate the individuality of the former, whereas 
in the topography both are as distinct as land and water. To preserve this 
distinction the Shinarump is denoted in the large scale maps by special 
modifications of the color, which are to be interpreted as meaning merely 
an arbitrary subdivision of the Trias. In the small scale maps, which are 
designed to express physical rather than stratigraphical facts, I have thrown 
the ShinArump into the Permian. 
The Permian beds consist of sandy clay-shales in very many thin beds 
and a few thin beds of impure limestone. They are very striking on 
account of their dense, rich colors, which are sometimes also wonderfully 
delicate. They are belted in a surprising way. Horizontal streaks of 
chocolate, purple and red- brown are interstratified with violet, lavender, and 
