Naga a eS SO see ae 
1886. | Super-Metamorphism and Vulcanism. 1007 
Without arguing this point further, I desire to present here 
some facts which seem to indicate that true Palzozoic strata have 
in one region (S. W. Colorado) become involved in the zone of 
metamorphism; that is to say, super-metamorphism has oc- 
curred. All along the Rocky Mountain chain to the north- 
ward the Silurian beds are recognizable, although I have seen 
them very much baked in portions of Northwestern Wyoming. 
The same succession of strata from top to bottom of the Palzo- 
zoic is discernible southward, as a rule, until we strike the great 
loop of the continental divide in the San Juan mining region, 
where the sedimentary formations skirt the base of the Quartzite 
mountains of Hayden’s survey. Here the Carboniferous and 
the underlying Devonian are well represented, and insignificant 
remnants of supposed Silurian strata occur zm situ. In some cases 
these last-mentioned rocks shade down gradually from the un- 
modified sédiments to the completely metamorphosed layers, and 
occasionally the Devonian limestone is so intimately connected 
with the subjacent granite as to form a continuous block of the 
two rocks welded together into one mass. Beneath the granites 
is a vast formation of quartzite, and the whole section studied by 
itself and in connection with the succession of strata in the 
adjoining country, seems to me wholly inexplicable upon any 
other theory than that of super-metamorphism, involving a con- 
siderable thickness of the early Palaeozoic beds, including nearly 
all of the Silurian formation. 
This idea, although worked out independently by myself, was, 
I find, entertained some years ago by Dr. Endlich, who passed 
rapidly over a part of the region in 1874. The importance of the 
fact, if such it be, of this super-metamorphism appears very evi- 
dent when we come to study the history of vulcanism in Colo- 
rado and Wyoming. From observations by the writer in the lat- 
ter area, in 1873, there seems no doubt that very similar condi- 
tions have existed in that great focus of eruption, although the 
results have been there much obscured by the lava flows and less 
disclosed by subsequent erosion. 
Referring to the preceding remarks on super-metamorphism, 
we may understand how, with a crust offering excessive resistance, 
| othe igneous fusion may be longer continued than in the case of a 
_ Volcanic eruption like those of the early Tertiary in the West or 
the Hawaiian initial outflows, all of the andesitic type. Von 
Richthofen’s series, as exemplified in the order of succession of 
