26 FAIRBANKS AND RAMPART QUADRANGLES. 
material from which the rocks are derived has a wide range of chemi- 
cal composition, and the rocks that result from its solidification pre- 
sent a great variety of mineral composition and many gradational 
.types. Therefore, no hard and fast lines can be drawn between the 
kinds of igneous rocks resulting from solidification through more or 
less complete crystallization. Furthermore, some of the igneous 
rocks, since their solidification, have been greatly changed by rheta- 
morphism along with the sedimentary rocks with which they are 
associated, and their original characteristics have been more or less 
obscured by the processes that have altered them. For the purposes 
of this brief report the igneous rocks of this area need to be con- 
sidered only in a very general way. For sake of convenience they 
are divided into granitic rocks, monzonitie rocks, greenstones', and 
basalts. 
GRANITIC ROCKS. 
Intrusive biotite granite and hornblende granite occur in parts of 
the Fairbanks region, notably in the ridge south of Gilmore Creek, on 
Twin Creek, Pedro Dome, and at the head of Chatham Creek. The 
rock of some of these localities is porphyritic with feldspar crystals 
an inch or more in diameter, and that at other localities is fine and 
even grained. The rocks are fresh and nave not undergone the 
metamorphism that has altered the schists. Intrusive gneisses, such 
as are common in the Fortymile region, were not observed, nor are 
the injection zones that are so common in the Fortymile country pres- 
ent in this western part of the Yukon-Tanana region. There are a 
few areas of coarse-grained biotite granite in the northern part of the 
region, near the head of Beaver Creek and between Beaver and Vic- 
toria creeks. Another area is located on the southern side of the 
divide, near the head of the Tolovana drainage. These intrusive 
masses were probably injected during Mesozoic time. 
Granitic rocks are not of common occurrence in the Rampart region. 
The most extensive mass observed forms a part of the summit of 
Wolverine Mountain, where it occupies an area about 1,000 feet wide. 
It is a porphyritic, massive, gray rock composed chiefly of quartz, 
phenocrysts of orthoclase a half inch or more in diameter, consider- 
able plagioclase, some biotite and hornblende, and a little pyroxene. 
The rock is finer grained toward the margin; the slates in contact 
with it have been indurated, and their fracture surfaces are flecked 
with the products of metamorphism, chiefly andalusite. 
A similar rock occurs west of the mountain near the saddle where 
the trail passes through the ridge to descend toward the Hutlina. 
This is also a gray porphyritic rock, but the porphyritic feldspars, 
some of them an inch or more in diameter, have a tabular develop- 
ment. The proportion of pyroxene is greater, there is less quartz, 
