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DIABASE.

Distribution. Along the north coast of Moresby island,
and on the southeast end of South island there are considerable
areas in which outcrops of diabase are found.

Iuithology. The diabase is a dark, greenish-grey medium-

grained rock, usually massive, and altered in appearance. Its
diabasic texture is not always apparent in the field, and it might
there be called a diorite or gabbro.

Structure. The diabase as seen in outcrops is a massive,
jointed rock, which gives no evidence of internal structures.
Small rounded darker patches occur in it, and are probably
segregations of the dark minerals.

Contacts of the diabase with the Maude formation were
observed in several localities. Most of these contacts showed
discordant relations between the diabase and the sediments;
but at one locality for several feet the relations were concordant.
The diabase is finer-grained near the sediments and includes
fragments of the argillite and limestones; it is, therefore, intrusive
into the Maude formation. The form in which it occurs is not
known, but the contacts and the texture seem to indicate that
it may be laccolithic.

Origin. This diabase is a hypabyssal, igneous rock, formed
by the cooling of molten magma at a moderate depth in the
earth’s crust.

AGE AND CORRELATION OF BATHOLITHIC ROCKS.

In regard to the age of the batholithic rocks of Graham
island it can only be said that they are post-middle Jurassic, and
pre-Upper Cretaceous. They are thus upper Jurassic or Lower
Cretaceous in age. As the rocks bear a general resemblance to
the granitic rocks of the Coast Range batholith, they may be
correlated with this great intrusive mass with a considerable
degree of certainty. The Coast Range batholith is generally
considered to be of upper Jurassic age.

The batholithic rocks of Graham island occur in relatively
small, separated areas as they do on Vancouver island.! It has

1 Clapp, C. H., Geol. Surv., Can., Mem. 13, 1912, p. 113.
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