114 BULLETIN OF THE 
side of a small pond, locality 21/. The great fault that uplifts the erys- 
tallines on the eastern border of the Triassic formation passes close to the 
southeast of this ridge, and is probably the cause of the reversed dip of its 
sheet and of the local fracture and overturning that it exhibits.1_ Trap 
generally porphyritic and glassy ; dense at the lower contact ; several 
exposures of fault breccia with the sandstone (Fig. 17); trap sends 
minute tongues of pure glass into lower sandstone, and occasionally en- 
closes grains of quartz and feldspar. Highly cellular at upper surface 
on northwestern slope ; its junction with sandstone above is not marked 
by local close texture ; sandstone immediately above contains numerous 
fragments of vesicular trap ; intercalated beds of shale and trappy con- 
glomerate occur near base of sheet. 
Locality 22. Section numbers, 51-33, 40, 73, 78. Ridge near Middlefield Station, 
Air Line Railroad. Percival’s Report, pp. 355, 856. Percival’s notation, P. 2 (S), 
E. IIL. (3). 
This posterior is traceable for several miles on the east of Durham 
Mountain, but the only satisfactory exposure is in a railroad cut, a little 
way west from Middlefield station, Air Line Railroad. Base of sheet 
sub-amygdaloidal as a whole, and locally very vesicular and uneven ; 
subordinate intercalated layers of trappy shale and irregular masses of 
abundantly vesicular trap near base; some vesicles filled’ with clastic 
grains of quartz, feldspar, muscovite, and fragments of glassy trap. 
Upper surface very vesicular. Trap generally glassy and porphyritic. 
Locality 23. Section numbers, 24, 25, 72. Falls of the Aramamit River. Percival’s 
Report, pp. 854, 355. Percival’s notation, P. 2 (N), E. III. (4). 
This is probably on the same posterior ridge as the preceding, although 
its direct connection has not been traced. Rock Falls Station of the 
Air Line Railroad is close by (Fig. 9). Trap generally glassy and por- 
phyritic, and not locally close-grained at junction with overlying rock. 
Upper surface extremely vesicular, with many vesicles filled with clastic 
material connecting with the main mass of sandstone above by narrow 
necks. Trap grains mixed with trap fragments at contact and for sey- 
eral inches above. A beautifully water-worn pebble of trap was found 
imbedded in the sandstone several feet above the sheet. Drift boul- 
ders in railroad cut near by show contacts and mixture of trap and 
sandstone. 
1 Amer. Journ. Science, XXXII., 1886, p. 847; Bull. Museum Comp. Zodl., Geol. 
Series, II., 1889, p. 72. 
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