52 
tige of dike rock to be seen % situ; nor does it appear to be 
chiefly due to faulting, but rather to rapid erosion along a series 
of close parallel joints. There has been a little slipping, how- 
ever ; for on tracing the thin bed of tuff across the one-hundred 
feet of beach, we find its outcrop shifted about twenty feet to 
the south, indicating an upthrow on the east of perhaps five 
feet. The melaphyr between the two walls, may, of course, 
have dropped down almost any amount, producing two con- 
verging and compensating faults. East of the beach the bed of 
tuff already described crosses the ledges diagonally to the shore 
in about one-hundred feet, passing out of sight under the water 
without any sensible change of dip or thickness. 
Returning to the west side of Valley Beach, the melaphyr, 
nine feet in thickness, overlying this tuff is found to be quite 
conformable, the contact showing only the minor irregularities 
that would naturally be developed where a stream of lava flows 
over unconsolidated sand and gravel. The contact is not 
always a sharply defined line, but the lava is enough mixed 
with the sand so that the two rocks are blended through a 
thickness of several inches. The swelling curves characterizing 
the lower surface of the tuff are not observed above it. 
The structure of this melaphyr, which is really the third 
flow, reckoning from the conglomerate on Long Beach Rock, is 
quite peculiar. A compact, greenish matrix encloses irregu- 
larly rounded amygdaloidal masses from two inches to two feet 
in their longest dimensions. The amygdules are usually ar- 
ranged in concentric lines or zones parallel with the exterior ; 
and the coarsest amygdules are sometimes towards the periphery 
and sometimes in the centre. ‘These masses are quite clearly 
distributed in irregular lines parallel. with the bed ; and this fact, 
as well as the great number of the masses, is decidedly unfavor- 
able to the view that they are true voleanie bombs. But the 
best explanation which has occurred to my mind is, perhaps, 
not wholly satisfaetory, viz., that, during the flowing of the 
lava, vesicular layers and crusts were, by the unequal flowing 
and revolving motions, broken up and the fragments rounded 
