676 WHITMAN CROSS 
in turn can be correlated with the Aubrey. The Manzano fauna 
comprises a certain number of species which occur also in the Rico, 
together with others not yet found in the Rico, which are more or less 
characteristic of the Aubrey.t' There is also some confirmation of 
the relations thus suggested in the fact brought to my attention by Mr. 
Girty that the Hermosa fauna bears a noteworthy resemblance to 
that of the upper part of the Red Wall limestone of the Grand Canyon, 
while markedly different from that of the Aubrey. No great emphasis 
can be laid upon this at present, however, since the collections upon 
which Meeks’ list of Red Wall forms given to Gilbert (14, p. 178) 
have been lost and further study of the Red Wall fauna is necessary 
to elucidate this matter. There is clearly a field requiring much 
further investigation as to the relations of the Red Wall, Aubrey, 
Hermosa, and Rico faunas. 
THE PRE-CAMBRIAN COMPLEX 
The ancient rocks of the Uncompahgre Plateau were described 
by Peale as in the main granites and gneisses with a subordinate 
amount of various schists. He called them Archean, considered them 
to be derived by metamorphism from sediments, and correlated them 
with the complex so well exposed in the Canyon of Gunnison River 
to the east (29). 
There is every reason to suppose that the rocks in question do 
belong to the same great pre-Cambrian complex which is well known 
in other parts of Colorado. Our limited observations in Unaweep 
and West Creek Canyons and at other points indicate that the old 
rocks of the Uncompahgre Plateau are comparable in most elements 
with those of the Needle Mountains and the Gunnison Canyon. 
There are many gneisses and schists, the origin of which is not wholly 
evident. Some gneisses are granitic in composition and may plausibly 
be considered as mashed or sheared granite. But there are many 
very dark hornblendic schists and others containing both horn- 
blende and biotite. Such gneisses and schists are probably the 
oldest rocks of the district and are naturally referable to the Archean. 
The gneissoid and schistose rocks are cut by many bodies of coarse 
1 The relations of the Manzano group will be discussed in a forthcoming bulletin 
of the Survey by W. T. Lee and G. H. Girty. 
