abstracts: geology 6oi 



Greenstones of a rather wide range in composition and origin make 

 up a large proportion of the metamorphic rocks. Closely associated 

 with the greenstones are slates, quartzites, and conglomerates and 

 many intermediate rock types. The greenstones appear to have suf- 

 fered the most intense changes, but secondary structure has developed 

 in the sediments also. Undeformed acidic dikes cut both the green- 

 stones and the sediments. It is tentatively assumed that the green- 

 stones, including the tuffs and some conglomerates which occur with 

 them, are of late Paleozoic age and that the sedimentary rocks are the 

 metamorphosed equivalents of the Cretaceous beds found elsewhere 

 in this region. 



Cretaceous rocks were found on Anvik and Andreafski rivers and 

 probably occupy much of the intervening area. More or less closely 

 associated with the Cretaceous rocks in the northern and eastern parts 

 of the region are a series of tuffs and flows of intermediate basic types. 

 Some of the flows appear to be intercalated with the Cretaceous sedi- 

 ments. In the southern part of the region are a number of dacitic 

 porphyry dikes of late Cretaceous or post-Cretaceous age. 



No sediments of known Tertiary age were found in the area, but at 

 somewhat widely separated points vesicular lavas occur as undeformed 

 horizontal flows which are either late Tertiary or early Quaternary. 

 Quaternary deposits are found throughout the region. 



At the beginning of the Quaternary period the surface stood at a 

 somewhat higher elevation than now, and the base-level of erosion 

 was lower, so that many of the streams were able to carve deeper 

 valleys in bedrock than those they now occupy. It appears likely 

 that the stream systems had become well established and a fairly 

 mature topography had been developed. At some time in this stage 

 of erosion there was an extravasation of basaltic lava which materially 

 altered the courses of sonic of the larger streams, possibly including 

 the Yukon itself or its predecessor. 



The report concludes with a discussion of the mineral resources of 

 the region. R. W. Stone. 



