53 
Into the forms we now see. East of Valley Beach, along the 
north front of Centre Hill, this melaphyr expands rather rap- 
idly ; and it is very obvious that while the rounded amygdaloid- 
al masses or pseudo-bombs are thickly and pretty uniformly 
scattered through the middle and upper parts of the flow, they 
are almost entirely wanting in the lower part. "They continue 
to form a prominent feature of the upper part of the melaphyr 
about half way across Centre Hill, and then die out rather 
gradually. Beyond this point the identity of the melaphyr as a 
Separate flow is lost, since it is indistinguishable from the over- 
lying melaphyr, with which it is here in direct contact. That 
the third melaphyr actually extends quite across Centre Hill, if 
not across Gun Rock, there can be no reasonable doubt. This 
flow is of exceptional interest, not alone on account of the 
pseudo-bombs, but also because it affords, perhaps, the only 
Instance in the Nantasket area where the tapering edge of a bed 
of lava сап be clearly traced. It certainly thins out rapidly 
toward the west, and, as stated, can not be followed much 
шше than two hundred feet west of Valley Beach, the under- 
lying and overlying tuffs appearing to come together at this 
point. Tt will not escape attention that the amygdaloidal 
Masses are thus found where we should most naturally look for 
them — in the marginal and superficial portions of the flow. 
The second bed of tuff in the Valley Beach section, or that 
overlying the amygdaloidal melaphyr, is lithologically similar 
to that below the melaphyr ; but it is three times as thick, and 
сап be traced westward the entire length of Atlantic Hill, with 
DO sensible change of dip or thickness, passing under the 
beach on the west where the County or Beach road first 
Teaches the base of the hill. It is well exposed near the Atlan- 
tie House steps, just above the bath house; from here it con- 
"nues around the hill a little above the middle of its height ; 
and then gradually descends to the level of the beach on the 
Cast. The continuity of the bed is clear; but its strike must 
change from N. 65° E. on the west to at least N. 75° or 809 E. 
OH Ае бакы s ç 
the east side of the hill. Its upper and lower contaets are 
