CHICHAGOF COVE 79 
second ridge, giving a synclinal structure to this part of 
the area. 
Concerning the fossils collected from this formation, Dr. 
Dali, to whom they were submitted for study, says: “ The 
fossils from the Stepovak beds are Eocene, probably of 
about Claiborne age (middle Eocene), and the only typical 
Eocene yet discovered in Alaska.” The description of 
these fossils by Dr. Dali and a discussion of the place of 
the Stepovak Series in the Alaska geological column will 
be found elsewhere in this volume. 
THE IGNEOUS ROCKS 
The Laccolith 
The intrusive rocks which have invaded the beds of the 
Stepovak Series are in the form of numerous dikes and a 
large laccolithic mass from which the dikes appear to 
radiate. The laccolith is well exposed near the summit 
of Chichagof Peak on the eastern side, the only point of 
the crest of the plateau which was reached. The dia¬ 
grammatic section, fig. 18, shows the relations that could 
there be observed. A general view to the north from the 
summit of the mountain gave the impression that the 
igneous rocks formed an extensive mass, the observed 
section lying on its extreme southeastern periphery, and 
therefore giving an inadequate idea of the bulk of the in¬ 
trusive matter as compared with the sedimentary rocks. 
The material of the laccolith is chiefly diorite-porphyrite, 
with small amounts of augite-diorite-porphyrite. It is a 
dark-colored rock, grey to greenish grey, and rather fine¬ 
grained, with distinctly prophyritic texture. On weathered 
surfaces the phenocrysts of hornblende stand out in relief 
and give the rock a very rough surface. The character¬ 
istics of the rock in its various phases may best be learned 
from the descriptions which follow of particular specimens. 
