114 BULLETIN OF THE 



side of a small pond, locality 21'. The great fault that uplifts the crys- 

 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.-' Trap 

 generally porphyritic and glassy ; dense at the lower contact ; several 

 exposures of ftiult 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, 31-33, 40, 73, 78. Ridge near Middlefield Station, 

 Air Line Railroad. Fercival's Report, pp. 355, 356. Percival's notation, P. 2 (S), 

 E. m. (3j. 



This posterior is traceable for several miles on the east of Durham 

 Mountain, but the only satisfactory exposui'e is in a railroad cut, a little 

 way west from Middlefield station, Air Line Railroad. Base of sheet 

 sub-araygdaloidal 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. 



Local'itij 23. Srrtion numbers, 24, 25, 72. Falls of tlie Aramamit River. Percival's 

 Report, pp. 354, 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. Eock 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 sev- 

 eral inches above. A beautifully water-worn pebble -of ti-ap 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., 18SG, p. 347 ; Bull. Museum Comp. Zool., Geol. 

 Series, II., ISbO, p. 72. 



