21 



Intrusives east of the Coast Range. The volcanic 

 and sedimentary rocks bordering the Coast range batholith 

 on the east up to and including the Skeena formation are 

 repeatedly intruded by stocks, some of large size, very 

 similar in mineralogical composition to the batholithic 

 rocks, and classed generally as granodiorites. The 

 ordinary variety is a greyish medium grained, massive 

 rock usually granular in texture, but often becoming por- 

 phyritic. Dark diorite and light coloured acid porphy- 

 ritic phases are not uncommon. 



These stocks probably belong to the closing stages of 

 the prolonged period of vulcanism in which the long Coast 

 range group of batholiths was intruded. They cut rocks 

 of Lower Cretaceous age, but are not known to intrude the 

 overlying Tertiary rocks. 



Glacial and post-Glacial Deposits. The district at 

 the height of the Glacial period was covered everywhere up 

 to an elevation of about 6,000 feet (1,828 m.) by a great 

 confluent ice sheet. The general movement of the ice 

 east of the Coast range was southerly, but a hugh stream, 

 as shown by numerous strong groovings along the mount- 

 ain slopes, poured westward to the sea down the valley of 

 the Skeena. 



At the close of the Glacial period, the district was 

 depressed, and Skeena valley was occupied by a long arm 

 of the sea which extended through the Coast range into 

 the Interior region. Since then there has been a gradual 

 elevation of at least 500 feet (152.4 m.), the sea has re- 

 treated and the mouth of the river has progressed steadily 

 down the valley. 



The deposits, illustrative of these changing conditions, 

 consist of boulder clays, estuarine clays, sands and gravels, 

 and fluviatile sands and gravels. 



The boulder clays in the lower portion of the valley 

 have been largely destroyed or buried up to Mile post 160, 

 a short distance below the mouth of the Kitsequecla river. 

 Above this point, the valleys of both the Skeena and Bulkley 

 are covered with a nearly continuous irregular sheet thinning 

 out on the ridges and deepening in the depressions. In 

 places, the sheet attains a thickness of over 200 feet (61 m.). 

 The common variety is dark in colour, exceedingly plastic, 

 and thickly packed with scratched boulders and pebbles. 



