MUSEUM OF COMPARATIVE ZOOLOGY. 113 



with scorise at contact with upper sheet. No local close-grained texture 

 at upper contact. 



Upper slieet dense as far as exposed in quarry ; becomes somewhat 

 fine-textured at contact with lower sheet ; its original upper surface not 

 seen in the quarry, but half a mile northeastward on the east side of the 

 ridge, locality 19' (Fig. C), the trap becomes vesicular. Several lines of 

 fault breccia traverse the quarry, consisting of large and small angular 

 fragments of trap contained in apparently unstratified sandstone ; often 

 slickensided ; the trend of these breccias agrees with that of the neigh- 

 boring faults, as determined by stratigraphic evidence. See special 

 account. 



No other significant exposures of the main sheet have yet been found 

 in its further northward extension in Connecticut. 



Division III. Posterior Ridges. 



Locality 20. Section numbers, 34-37, 74, 75. First ridge posterior to Saltonstall 

 Mountain. PercivaVs Report, p. 324. Percivai's notation, P. 1, E. I. 



The upper surface of this posterior ridge is exposed only near its 

 northeastei'n end, at a road crossing, about a mile northeast of Salston- 

 stall Pond (Fig. 11). Elsewhere the outcrops are generally dense, but 

 sometimes vesicular on the back of the ridge. 



Upper portion of sheet very vesicular and glassy ; not locally close- 

 grained at junction with overlying sandstone ; sand' grains and trap 

 fragments occur together at upper contact ; sand fills vesicles in trap ; 

 occasional water-worn fragments of trap in the sandstone a foot or more 

 above the sheet ; base of sheet sub-amygdaloidal. 



Eidges of very coarse trap conglomerate occur in the neighborhood, 

 but their relation to this sheet is not yet clearly made out. 



Locality 21. Sectton yuimher, 18-23, 187-19.". Second ridcre posterior to Saltonstall 

 Mountain. Percical's Report, p. u25. Percivai's notation, V. 2, E. I. 



According to our interpretation of the stratigraphy, this ridge is a 

 second outcrop of the sheet already seen in the first posterior, here 

 showing a western dip, as if on the eastern side of a synclinal ; its base 

 is open in several small abandoned quarries near a road crossing, lialf a 

 mile northwest of Brauford station. Shore Line Railroad, locality 21 

 (Fig. 11) ; and its upper surface, with something of the overlying sand- 

 stone, is seen an eighth of a mile north of these quarries, on the eastern 



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