120 BULLETIN OF THE 
needles and brownish glass. As regards their origin the microscopic 
study yields no solution, but the field evidence leaves little doubt in the 
observer’s mind. The thin trap sheet overlying the lapilli is, wherever 
observed at this locality, more or less vesicular, and in many places 
cavernous. The greatest vesicularity is at its upper surface, and in the 
hand specimens from the contact with the sandstone above the sand is 
seen to have minutely penetrated the cavities and fissures of the scoria- 
ceous amygdaloid. The sand grains not only occupy surface vesicles, 
but they have percolated aiong cracks and irregularities in the trap to 
a depth of two feet below the surface ; in some cases, they apparently 
lie between or surround large areas of amygdaloid. Irving speaks of 
similar phenomena in connection with the upper surfaces of extrusions 
in the Lake Superior region, and refers to them as sandstone “ veins.” ? 
The lamination of the overlying sandstone is parallel to the surface of 
the trap, conforming closely to its minor irregularities. Flowage action 
is seen in the trap in the elongation of its vesicles. 
An interesting point is the occurrence of two thin layers of tufa in the 
sandstone just above the trap, each about an inch in thickness and about 
a foot apart. These layers appear in the hand specimen of a rusty brown 
color, composed of water-worn fragments of trap mixed with clastic quartz, 
and have a much weathered appearance. Under the microscope their 
tufaceous character is well shown; vesicular porphyritic trap grains 
abound, and others of non-polarizing character are derived from yellow- 
ish glass, now partially or wholly devitrified. Mixed with the trap frag- 
ments, there are abundant grains of quartz, muscovite, and orthoclase, 
probably derived from the crystalline rocks which surround the Triassic 
formation. The tufas as well as the sandstone effervesce readily with 
dilute hydiochloric acid, owing to the presence of secondary calcite. 
The sandstone owes its dark color in a large part to the presence of 
comminuted dust-like particles of extremely weathered trap, scattered 
through it and now altered to earthy chlorite and fine dots of ferrite. 
The several well-marked features of this interesting locality leave 
no doubt that the trap sheet here is of extrusive origin. 
Hartford City Quarry. Locality 26.—One of the posterior sheets, as 
yet not safely correlated with other outcrops, forms a ridge of moderate 
height, with strong western bluff, in the southern part of Hartford, 
where it is extensively quarried for road material. Trinity College 
stands on its eastern slope. 
1 Copper-Bearing Rocks of Lake Superior, Monogr. V., U. S. G. S., 1883, p. 292. 
