144 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



]ying members of the Summit series, must have been formed from the ruins 

 of coarse-grained, granitic rocks which, in post-Irene time, became exposed 

 to erosion within this region. This contrast between the lower and upper 

 formations of the series i9 particularly noteworthy in the case of the absence 

 of clastic microperthite in the conglomerate, while that mineral is a prominent 

 clastic component of the Wolf grit and still younger members of the Summit 

 series. From the fact that this peculiar feldspar occurs in the oldest exposed 

 beds of the Lewis, Galton, and Purcell series, there is already good presumptive 

 evidence that the Irene conglomerate has no stratigraphic equivalent in the 

 ■eastern series. There is abundant corroboration of this view in the general 

 stratigraphy, as will be noted in the section on correlation. 



Irene Volcanic Formation. 



The Irene conglomerate is conformably overlain by a great mass of lava 

 flows which, for a thickness of a hundred feet or more, are interbedded with the 

 conglomerate. These lavas crop out along the western slopes of Irene moun- 

 tain, and they may be grouped under the name of the Irene Volcanic formation. 

 As with all the other members of the Summit series, the band of lavas may 

 be followed from the Boundary line northward across nearly, the whole width 

 of the ten-mile belt. The northern extremity of the band occurs at the cross- 

 cutting contact of the Bayonne granite batholith. Complete sections were 

 measured on the Dewdney trail, on Irene mountain, and on the ridge south 

 of Monk creek. The best exposures of the formation as a whole were found 

 in the last mentioned section. 



The formation chiefly consists of a large number of thick basic lava flows, 

 in which a few subordinate layers of basic tuff, a thick band of conglomerate- 

 breccia, and a strong bed of dolomite are intercalated. 



Like the conglomerate and the overlying Monk schists the whole mass has 

 been greatly altered by dynamic metamorphism, with a general development of 

 marked schistosity. The massiveness of the flows and the prevalence of this 

 secondary structure render it often impossible to determine true dip at even 

 extensive outcrops. Nevertheless, the attitude of the original, layering has 

 been discovered at so many horizons that an important generalization can be 

 made, — the dip of bedding is always steep, varying from 70° E. to 70° 

 W., with strikes varying from N. 7° E. to 1ST. 30° E. Bedding and schistosity 

 planes are in most cases nearly or quite coincident. The outcrop of the forma- 

 tion averages nearly 1-5 miles in width. Assuming an average dip of only 70° 

 and considering the structure of the band as monoclinal throughout, the thick- 

 ness of the formation is at least 6,000 feet. High as this figure is, it must be 

 regarded as the smallest allowable estimate. Extensive duplication of the beds 

 I>y folding or faulting within the area is highly improbable. The bed of con- 

 glomerate-breccia was followed for at least eight miles, through which distance 

 it preserved its thickness, high dip, and proper horizon below the base of the 

 Monk formation. The breccia and the associated dolomite are conspicuous 



