40 USAGI, (Cy die GS SIEILIL 
southwest of about eight miles, and a width of two or three 
miles. Its surface consists of high, rounded, grass-covered hills, 
with little or no timber, and from this rise the two or three more 
elevated points to which the name Warren peaks has been 
applied. These more central points are surrounded by smaller 
and less prominent peaks, which are separated by deep ravines 
or gulches forming the lines of drainage. Besides this great 
nucleal mass of igneous rock, several outbursts, very local in 
character, were observed in the zone of encircling strata. The 
rock is a trachyte, dark gray in color, and containing frequently 
large and perfect crystals of sanadine which give it a porphy- 
ritic character. Small crystals of mica and hornblende are also 
prominent, and the rock yields more to weathering than that of 
some of the other peaks. In different portions of the district 
the rock varies somewhat in its character, though evidently of 
the same general nature. 
The encircling zones of sedimentary rocks include the Pots- 
dam below and the Jura above. Their dip is quaquaversal and 
is usually quite regular, the angle varying from 20 to 30 degrees. 
The Potsdam sandstone which immediately overlaps the base 
of the igneous mass has been greatly metamorphosed. When 
the rock was shaly it has been changed into a hard fissile slate, 
scarcely recognizable as of sedimentary origin; and the pure 
sandstone strata have been converted into compact quartzite often 
of a very white color. In several places the igneous matter 
seems to have penetrated between the strata, which are scarcely 
distinguishable from the injected rock, and in many cases the 
metamorphosis appears to have been performed by the action of 
heated waters, for the sandstone was found penetrated irregularly 
by well-formed crystals of feldspar. On the west side, near the 
middle of the formation were found layers of argillaceous sand- 
stone covered by large branching fucoids peculiar to the Potsdam, 
and some of the upper layers of the sandstone are perfectly 
riddled with Scolithus holes. The Potsdam, Carboniferous and 
Red Beds are well exposed in many of the canyons which radiate 
from the central area carrying the drainage eastward to the Red- 
