i kindle.] GEOLOGIC SKETCH. 31 
is undetermined, though they are known to be older than the Devo- 
nian and therefore will fall in the lower Paleozoic or pre-Cambrian. 
RAMPART FORMATION. 
This formation also was described by Spun" 1 in the report to 
which reference has already been made. It includes limestones. 
quartzites, black slaty shales, cherts, green shales with interbedded 
tuffs, and a mass of igneous material, mostly serpentine, diabase, and 
line-grained fragment a] volcanics, which have imparted a character- 
istic green color to the formation. A problem arises in drawing the 
boundary between these rocks and those of greater age. In discussing 
the Fortymile formation the line was drawn between a quartzite- 
schist and a rather massive limestone. Several sections were observed 
where, in passing from schists believed to belong to the Fortymile 
formation toward the rocks that are characteristically Rampart, a 
limestone occurs closely associated with the green igneous rocks. Such 
a limestone outcrops just below the forks of Bryant Creek, where it 
forms a steep slope about '200 feet in height, contains some fine- 
grained chert-like, siliceous beds, and is in close contact with the green 
igneous rock. The ridge to the north of Excelsior Creek and along the 
north side of Mission Creek has at its base a low sharp ridge of 
quartzite-schist with quartz veins, which may possibly belong to the 
Fortymile formation. This is separated by a timbered hollow from 
the main ridge, Avhich is composed of gray limestone about 150 feet 
in thickness, capped by a very fine-grained, green, vesicular, dia- 
basic rock. This limestone, which forms prominent outcrops all 
along the steep slope toward Eagle, has frequently associated with it 
black shaly slates and is everywhere capped by the igneous rock. 
In the Fortymile region south of Eagle, between the graphitic quartz- 
schist and the green schists north of Thirteenmile camp, there is a 
limestone which occasionally yields fossils. Only crinoid stems were 
found, and these are of little stratigraphic value, but it is believed 
that this limestone, like those above mentioned, is more closely related 
to the green rocks than to those of the Fortymile formation. A dark 
ishaly limestone and dark shales occur also between the greenstone 
area south of King Solomon Creek and the metamorphic schists to 
the north of this creek. It is deemed best, in view of the little evi- 
dence at present available, to include all the rocks above described 
in the Rampart formation. The members of this formation have 
been metamorphosed far less than those of the Fortymile. They are 
well developed on American Creek and on the ridge to the west, from- 
ing a belt several'miles wide, with a northwest-southeast trend. This 
oelt crosses Bryant Creek just below the forks and covers a consider- 
Op. cit., pp. 155-169. 
