260 A. H. BROOKS — RECONNAISSANOES IN SOUTHEASTERN ALASKA 



Iii the Ketchikan district, Middle Devonian fossils were found at Long 

 island, Kasaan bay, Prince of Wales island, and at Vallenas bay, Gravina 

 island. The presence of Devonian fossils in these widely separated 

 localities goes to show that this period is probably well represented in 

 southeastern Alaska, At the Prince of Wales Island locality the Devo- 

 nian beds are almost entirely unaltered, and this rather unsafe criterion 

 has been used to differentiate them from the older white crystalline 

 limestone series. When more detailed examinations have been made, 

 it may be found that some of the crystalline limestones are of Devonian 

 age. These rocks of Devonian and Carboniferous age form the second 

 of the lithologic belts. 



The third belt in which the rocks have lithologic similarity lies west 

 of and adjacent to the Coast range. It consists of argillites, with some 

 limestones and a large amount of intrusive greenstone. It has been 

 recognized by the writer in the southern province and again in the 

 northern part of the province. Its age has not been determined, but it 

 probably includes both Carboniferous and Triassic rocks. Near the 

 contact with the granite, which latter is intrusive, it is often considerably 

 altered. 



The granite belt which forms the Coast range has already been referred 

 to. It is a batholitic intrusion of great extent which has been traced 

 for 800 or 900 miles. This intrusion probably took place in Triassic 

 times. While most of the granite is massive, it in places includes some 

 schistose and gneissoid phases. There are also outlying masses of granite 

 both east and west of the Coast range. 



The older sediments west of the Coast range. have been differentiated 

 into three groups, of which two are Paleozoic and one is probably in 

 part Paleozoic and in part Mesozoic. The corresponding series east of 

 the Coast range are all grouped together as Paleozoic. The writer has 

 only studied them along one section, and found it impossible to differ- 

 entiate them. 



In the southern part of the Alexander archipelago a heavy conglom- 

 erate was found overlying Upper Paleozoic rocks unconformably. These 

 are believed to be Mesozoic and probably Cretaceous, though no fossils 

 were found in them. East of the Coast range and in the Queen Charlotte 

 islands to the south Dawson and others have found beds of similar char- 

 acter, which are of Lower Cretaceous age. 



Large areas of extrusive rocks, probably of Mesozoic age (Cretaceous?), 

 were observed by the w T riter on Prince of Wales island. These are chiefly 

 of andesitic character, and are closely associated with intrusive rocks, 

 from which they can not always be easily differentiated. 



Tertiary sediments have been noted at a number of localities. They 



