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size up to 2 or 3 feet across, and irregularly flat in shape. The
groundmass of the rock is in all cases dense, and in many cases
considerably altered.

The filling of the amygdules is made up of various minerals,
in varying proportions. Some contain pale bluish-grey, chalce-
donic silica only; and these, when weathered from the rocks and
rounded on the beach, form the agates for which the locality is
noted. Others contain only calcite and, in the altered rocks,
chlorite. The fillings composed of single minerals are usually the
smaller amygdules, under an inch in diameter. A very common
type of filling, perhaps the most common, and one to which
the larger amygdules belong, consists of an outer rim of banded,
bluish-grey chalcedony lined with a concentric layer of inwardly
projecting quartz crystals which in some amygdules fill the whole
space and in others leave a cavity. It is in this central cavity
that the tar is found, filling the whole space; so that when the
amygdule is broken open on a cool day, the tarry, internal mould
may be seen to bear the imprint of the crystalline facets of the
quartz. One pint of tar has been taken from a single one of the
larger amygdules. In some of the smaller amygdules tar forms
the sole filling.

In the agglomerates tar occurs with calcite and quartz,
which form irregular replacement masses up to a foot or so across,
the tar filling cavities in the masses.

In both the amygdaloids and the agglomerates tar is found
in fissure veins. The vein filling is mostly chalcedony, quartz,
and calcite, usually with a symmetrically banded structure.
White, pale blue, or grey laminated chalcedony occurs on each
wall of the vein, the middle portion of which is composed of clear
quartz or white calcite crystals projecting inward; and tar is
found in the vacant space between the ends of the crystals.
The occurrence is thus seen to be essentially similar to that in the
amygdules. The veins are from a fraction of an inch to 3 feet
or more wide, and occasionally over a score of feet long, though
usually not attaining such length. They branch and reunite
and in general are irregular.

Liquid oil is said to occur in some of the agates from this
vicinity and in these a bubble can be seen to move through its