GENERAL GEOLOGY 47 



is lithologically like the Kadiak slates containing the fos- 

 sils here under discussion. It will be difficult for a long 

 time to separate these nearly barren beds, which are con- 

 nected by many lithological similarities, into a Triassic 

 and a Jurassic series, and I have therefore left the name 

 1 Vancouver Series ' to cover them all, with the limits of 

 usage given it by Dr. Dawson. 



SITKA 



The prevailing rock about the town of Sitka is a black 

 slate, often greatly crumpled and jointed. 



A very interesting and characteristic rock of this series 

 is the tuffaceous greywacke found in typical development 

 at the mouth of Indian River, near Sitka, and elsewhere 

 at many places on the island. It has the aspect of a firm 

 dark massive coarse sandstone, in which many of the grains 

 consist of fragments of other rocks. 



A slide cut from the rock at the mouth of Indian River 

 (203) proves it to be fine-grained indurated tuff, contain- 

 ing many clastic quartz grains, together with shattered frag- 

 ments of black carbonaceous shale, of a hyalopilitic andesite 

 groundmass, and of a darker ophitic eruptive, probably ba- 

 salt. It may be thought of as the product of explosive 

 eruptions, which shattered and mingled several kinds of 

 volcanic rocks with the sands and fragments of the muddy 

 beds, the clastic ingredients being indurated by the heat 

 of the eruptions in which they were involved, like the 

 modern shell marls enclosed in the tuffs of the Pribilofs, 

 already described. 



The beds at the mouth of Indian River were examined 

 with care. The massive tuffs contain many small angular 

 fragments of the black slate, which grow larger toward an 

 adjacent area occupied by shattered slates in which the 

 fissures are filled by small injected mud veins of the tuff 

 which accompanied the eruptions. The dip and strike 



