96 
The second flow of melaphyr begins with about fifteen feet of 
compact, green melaphyr overlain by five to ten feet, in one to 
several bands, of amygdaloidal melaphyr. It is similar to the 
first flow, except that the amygdules are not го crowded and 
the bands are not so well defined. These flows are strongly 
contrasted with, and undoubtedly much newer than, the flow 
forming the base of West Porphyrite Hill, one hundred feet 
away. The isolation of this outcrop makes an absolutely safe 
correlation impossible. It is reasonably certain, however, that 
it should be referred to either the upper or lower amygdaloidal 
melaphyr of the central area. It looks like a block detached 
from Melaphyr Plateau: in fact the lithological resemblance 
is almost perfect. And this view is strengthened by the low- 
tide ledges of precisely the same melaphyr which stretch away 
to the eastward, in the direction of Melaphyr Plateau, and 
virtually extend Melaphyr Peninsula as far as the base of Kast 
Porphyrite Hill. It is a foregone conclusion, then, that the 
short beach connecting Melaphyr Peninsula and West Porphy- 
rite Hill conceals an important fault with the downthrow to the 
north, an extension, apparently, of the line of displacement 
dividing the coastal and central areas. The slip can searcely be 
less than 150 feet, and may easily be 100 feet more. 
Rocky Neck. 
The part of Weir River Bay separating Rocky Neck from 
Nantasket is not a geological boundary; for the western shore 
repeats, with slight variations, the geological conditions with 
which we have become familiar on the eastern shore. These 
variations are, however, of some moment, since they supply miss- 
ing links in the chain of evidence essential to the correlation of the 
Nantasket strata. But although Rocky Neck is simply a de- 
tached part of Nantasket, we can go no farther west in the study 
of Nantasket geology ; for not only 1з a natural boundary pro- 
vided in the drumlins of World's End, Planter's Hill, and Pine 
