788 INDEX TO THE STEATIGEAPHY OF NOETH AMEEICA. 



Plant remains which have been obtained from this locaHty have all been deter- 

 mined by Knowlton to belong to the Kenai, or to be of upper Eocene age. The 

 exposures along the beach near Tyonek were described by Spurr ''^^ in 1900. The 

 Yentna and Hayes River beds of Spurr, which occur north of Tyonek on the lower 

 Susitna and in Skwentna Valley, are now also regarded as of Kenai (Eocene) age. 



P 6. MATANUSKA VALLEY. 



Matanuska River enters Cook Inlet at its northeastern embayment. It com- 

 prises a large area of coal-bearing strata classed as Kenai (Eocene) and described 

 by Paige and Knopf ^" as follows : 



The Kenai of the Matanuska . basin comprises a series of sandstones, shales, arkoses, num- 

 erous coal seams, and a large volume of conglomerate. The rocks are well indurated and, as 

 first noted by MendenhaJI, resemble the Paleozoic coal measures of the Appalachian region. 

 The sandstones are gray, hard, and tough and are characterized by the presence of silvery shreds 

 of white mica. At some localities, as in the leaf-bearing strata in the Kings Creek coal measures, 

 the sandstones contain shale fragments. The shales show no unusual features; they are dark 

 bluish, fissile, and interstratified with the sandstones in very regular beds. The arkoses were 

 noted only on the ridge north of Tsadaka Creek, abutting against the quartz diorite mass. They 

 are composed of feldspar, quartz, and chlorite and locally contain granite pebbles. Certain 

 strata are fine examples of regenerated granites. 



Conglomerate is found at Castle Mountain, between Kings and Chickaloon creeks, and at 

 Conglomerate Mountain, between Tsadaka and Eska creeks. At both places the deposit 

 is at least 1,000 feet thick. Thin sandstone beds, not exceeding a few feet in thickness, are 

 intercalated with the conglomerate and pinch out along the dip. The pebbles of the conglom- 

 erate are well worn and possess a weU-defined shingling. Their diameter averages 4 inches and 

 ranges up to 8 inches. Greenstone porphyries form the principal material of the conglomerate, 

 with some quartz prophyry and very rarely some granite and vein quartz. The matrix of the 

 pebbles is a grit. 



Heavy beds of conglomerate dipping to the north can be seen on the east side of Chickaloon 

 Creek. They are part of a great series of sandstones, shales, and conglomerates, probably not less 

 than 3,000 feet thick, which are overlain by basaltic porphyries at an elevation of about 4,700 

 feet. 



The coal of the Kenai of the Matanuska basin is bituminous except where modified by 

 igneous rocks. The seams vary in thickness up to a maximum of 17 feet. 



The age of these strata has been determined by Knowlton as Kenai (upper 

 Eocene) . Fresh-water gastropods have also been found in them. 



P 6-7. CONTROLLER BAY TO CAPE YAKATAGA. 



On the southern coast of Alaska, in latitude 60°, Tertiary sediments which 

 resemble the Kenai in character but may be younger have been examined on Con- 

 troller Bay and are known to extend east to Cape Yakataga. They have been 

 classified in several formations and described in detail by Martin/^^ who says : 



The Tertiary sediments * * * consist of monotonous repetitions of shales and sand- 

 stones, with an included mass of coal-bearing arkose and one or more massive conglomerates. 

 The total thickness, as shown in the following table, is many thousand feet. The structure of 

 the region in which these rocks outcrop is complex, exposures at critical points are often wanting, 



