45 



It includes rock formations representing nearly all the 

 geologic periods from early Paleozoic to the present. 

 The Paleozoic rocks have passed through several periods 

 of folding and metamorphism, and show clearly the effects 

 of such treatment. They are in places so intensely 

 metamorphosed and intricately folded, that it is not pos- 

 sible to disentangle all the details of their structure; even 

 to decipher their broader features is in many instances 

 not easy. In general the formations strike parallel with 

 the northwest trend of the mountain range, and this 

 produces a zonal arrangement of the broader features of 

 the areal geology. In the different formations, we find 

 interbedded with one another, black slates, argillites, 

 greywackes, crystalline schists, crystalline limestones 

 quartzites, greenstones, and chlorite- and amphibole- 

 schists. The intrusive rocks consist chiefly of granular 

 diorite and granite types. They constitute the great 

 batholithic core of the Coast range, and dominate it both 

 structurally and petrographically. They also cover large 

 areas in the central portions of many of the islands. 



The Coast Range batholith is bordered on the west by 

 a band, several miles wide, of closely folded crystalline 

 schists, composed largely of Carboniferous and Mesozoic 

 strata. They have been termed the Ketchikan series by 

 Brooks in the Ketchikan district, while in the Juneau 

 district they are grouped together as the "schist band" 

 by Spencer. They have been traced from the southern 

 boundary of Southeastern Alaska to its northern boundary 

 at the head of the Chilkat basin. These strata are 

 essentially siliceous mica-schists and argillites, feldspathic 

 schists with intercalated amphibole — and chlorite — schists, 

 and occasional belts of crystalline limestone containing 

 Carboniferous fossils. Narrow outlying belts of the 

 Coast Range intrusives invade these schists and have often 

 altered and recrystallized them to such an extent near the 

 contacts that they are now massive gneiss, and it is not 

 everywhere possible to distinguish with certainty the 

 boundary line between the intrusive and the intruded 

 rocks. This is especially true along the margin of the 

 mainland Coast Range batholiths, where, in addition to 

 gneissoid structure, the rocks are cut by an intricate 

 network of pegmatite dykes and quartz veinlets. In the 

 Ketchikan district this type of contact prevails, the effect 

 of the intrusive extending often for io miles, (16 km.) and 

 more out from the contact. Away from the contact, the 



