So-Callcd Basal Granite. — McCoiuicll. 59 
and underlies them." In a preceding paragraph, however, 
the same writer states "The possibihty still exists therefore 
that the granite may be intrusive, having broken through the 
sedimentary rocks in a massive body and dragged up the beds 
so that they lie on its flanks dipping away in all directions.' 
Air. Spurr in the body of his report refers constantly to the 
gneisses as the basal granite, but the reasons given for this 
conclusion are largely theoretical and it is evident from the 
passage quoted that he did not consider tjie question absolute- 
ly settled, n 1898 the lower White river and the Tanana 
were examined by Air. A. H. Brooks. The valleys of both 
these streams afford good sections of apparently the same 
gneisses or sheared granites found on the Yukon. Air. 
Brooks states that* "definite proof of the basal nature of this 
gneissoid series is still wanting. There is however strong 
evidence that the metamorphosed clastic series which lie ad- 
jacent to the gneisses are younger, and that the gneisses 
s.iould be regarded as basal." 
Rclatioiis/iip of Gneisses to Altered Clastics. 
During the past season the writer examined the Yukon 
valley from Fort Selkirk to Fortymile, and also spent some 
time in the Fortymile and Sixtvmile districts. The evidence 
obtained in this investigation all went to prove that the con- 
tact between the gneisses and the altered clastics is an erup- 
tiye one, and that the latter, so far as known, represents the 
basement formation of the district. The evidence consisted 
principallv in the alteration and deformation of the clastic 
schists near the contact with the gneisses or sheared granites, 
the inclusion of fragments of the clastic schists in the gneisses 
- and the occurrence of thin sheets of g-neiss alternating with 
the schists usually close to the borders of the lareer areas. 
In the Yukon valley and adjacent recfion the cneisses as 
stated previously alternate with the clastic schi.sts in bands and 
areas ranging from a few feet to twentv miles or more in 
width. The contacts between tiie two formations is usually 
concealed, but in a few places the relationship is clearly 
shown. A god example occurs on Fortymile river below the 
mouth of Brown creek. At this point the river cuts across 
tTwentieth Annual Report, V. S. Geo. Survey, Part VII, Page 465. 
