84 
as melaphyr on the map are of precisely the same kind as that 
just described, and are plainly parts of that flow. The tops of 
the ledges sometimes show traces of the overlying conglomerate ; 
and these prove a very perceptible westerly dip, as if the bay 
occupied here a faintly marked syncline. 
Melaphyr W. Porphyrite Granite ; 
N. Peninsula. Hn. Cliff Plateau. Plateau. ©. 
mg 
OC A 
SS OUR Ма 
TEM ER 
AN AREAS 
Granite. Conglomerale. Melaphyr. Porphyrite. 
Fic. 11.— SECTION FROM NANTASKET HARBOR ACROSS MELAPHYR PENINSULA, 
Wrst PoRPHYRITE HILL, AND CLIFF PLATEAU TO GRANITE PLATEAU. 
SCALE, I INCH — 400 FEET. THE DIKES ARE, FROM NORTH TO SOUTH, 
NOS. 28, 31, 34, AND 22. DIKE NO. 29 IS OMITTED. 
The conglomerate is mainly of medium texture, and becomes 
finer upward ; but at the base it is ina large part very coarse 
and irregular. The contact with the melaphyr, although so 
perfectly exposed, is somewhat obscure and indefinite, because 
the conglomerate fills the numerous cracks and marked inequal- 
ities which naturally characterize the upper surface of the mela- 
phyr flow ; and also because at its base the conglomerate is 
largely, in some cases almost wholly, composed of melaphyr 
debris. Very few of the fragments and pebbles of melaphyr 
are amygdaloidal ; and they can nearly all be certainly referred 
to the subjacent bed. Near the base of the conglomerate, es- 
pecially, many of the component fragments are exactly like the 
melaphyr which it rests upon. It would, perhaps, be difficult 
to find a clearer example of a contemporaneous lava covered by 
newer sediments. The relations of the two rocks are simply 
inexplicable on the theory that the melaphyr is intrusive. 
Along the contact, especially, granite is very abundant in the 
conglomerate ; and several masses were noticed from one to 
three feet in diameter, the largest ones resting directly upon 
the melaphyr, or seeming to be almost imbedded in ite. Tho 
