84 ALASKAN MINERAL RESOURCES IN 1906. 
the same rocks. • The contact between this series and the older sys- j 
terns has not yet been discovered, but may be looked for near the head 
of Ustay River. East of that general vicinity the mountains are 
composed chiefly of the preceding series. The Yakutat rocks are 
distinguished from those previously described mainly by a general 
absence of the effects of metamorphism. The predominant rocks \ 
are graywackes and black clay rocks which are slates or shales accord- j 
ing to locality. Many of the graywackes are conglomeratic, the con- 
glomerates being internal rather than basal. The pebbles consist of ] 
black slate, dark graywackes, limestone, granite, schists, etc. 
The stratigraphic succession within the Yakutat series was not defi- 
nitely ascertained, for the structure of the beds is so complex as to] 
defy analysis without detailed mapping. The writer's present inter- 
pretation of the structure suggests 'that the section is roughly as] 
follows: 
2. Slates or graywackes of black and gray color, with local beds of coarse and fine con- 1 
glomerate. Some of the graywacke members are 200 to 500 feet thick. 
1. Bowldery slates — black strati lied rocks containing pebbles and bowlders of all 
sizes and various compositions. 
Only the lower member of this section requires further mention. 
This bowlder deposit consists of black shale or slate in which strati- 
He at ion is usually distinct. Pebbles and bowlders are scattered 
through it without orderly arrangement. In size they vary from 
fine gravel to bowlders at least 100 feet in diameter; in composition 
they include varieties so widely different as granite, white limestone,? 
greenstone, graywacke, and quartzite. Although irregular in form, I 
the bowlders are generally roundish or subangular. They have not 
the well-rounded contours characteristic of waterworn stones. The 
general character of the deposit suggests that it may be an offshore 
formation over which floating icebergs strewed their debris at random. 
Fossils are rare in the Yakutat series and are of unsatisfactory 
nature. Those found consist chiefly of jointed stemlike casts, a 
which may represent plants or possibly worm trails. None are of 
much value for purposes of correlation with the terranes of other 
regions. 
GLACIAL DEPOSITS. 
In view of the great development of glaciers, both now and in the 
last geologic epoch, it is, on first thought, rather surprising that 
more extensive deposits of drift are not found in the Yakutat region. 
The moraines along the east side of Yakutat Bay, stretching out to 
Ocean Cape, have been described by Tarr and Martin. 6 There ap- 
pears to be another loop of drift concentric with the south end of 
a For similar varieties see Ulrich, E. O., llarriman Alaska Expedition, vol. 4, 1904, pp. 125-146. 
b Tarr, It. S., and Martin, Lawrence, Bull. Am. Geog. Soc, vol. 38, 1906, pp. 155-160. 
