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MUSEUM OF COMPARATIVE ZOOLOGY. 129 
presence of augite, the lower sheet would be classed as a glassy form 
of augite-porphyrite. 
The texture of the rock steadily grows finer, and the cavities due to 
gas expansion more numerous, as we approach the surface of junction 
with the upper sheet ; and there is at the same time a marked increase 
in the amount of glass forming the base. At five feet below the contact 
the vesicles occupy nearly one fourth of the space, and in slide 140 of 
our collection they are seen to be elongated parallel to the surface of 
contact, as if indicating flowing action. The origin of the vesicles by 
gas expansion is beautifully shown in this slide by the well marked 
tangential arrangement of the feldspar crystals about the elongated and 
tortuous amygdaloidal cavities, conforming even to their minor irregu- 
larities. Sections from the red seam, just under the junction, show 
this portion of the trap to have been blown almost to shreds by the 
escaping gases. The scoriaceous character here cannot be doubted ; 
fully two thirds of the rock is made up of secondarily deposited calcite 
and quartz, filling the irregular cavities and vesicles of the porous mass. 
The inter-vesicular areas consist of a greenish glass, thickly sprinkled 
with hair-like microliths of feldspar and an occasional porphyritic crystal 
of the same. ‘The red color of the seam is due to the formation of iron 
sesquioxide. Hawes noted that the oxidation of iron-bearing minerals 
exposed to surface weathering is from the protoxide to the sesquioxide 
state, while the change is from one protoxide to another when not thus 
exposed, as is true of the eastern ranges.’ It therefore seems likely that 
in this instance the red color of the surface of the lower sheet indicates 
surface weathering before the upper sheet was erupted, thus confirming 
the suggestion already made, that the thickness of the flow was great 
enough to raise its surface above water. It is rare that this red color is 
seen in the traps of the Triassic area. 
The scoriaceous character of the sheet at its upper surface is much 
more strongly marked than in others thus far examined in the Connecti- 
cut valley ; this is also thought to be connected with the appearance of 
the surface of the sheet above the surface of the body of water into 
which it flowed. Cooling under the air must have taken place much 
less rapidly, and under much less pressure, than when below the water 
surface, thus permitting a more complete expansion of the occluded 
gases and the production of a highly pumiceous surface layer. 
The trap of the upper sheet just above the red seam appears in the 
hand specimen much less altered than that from below. Even at the 
1 Amer. Journ. Science, IX., 1875, p. 190. 
VOL. XVI. — NO. 6. 9 
