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turbed, is exposed again. The general line of strike is 

 evidently east-west, and the bed has a greater extent in that 

 direction than is indicated on the map. A similar grayish 

 and slightly arenaceous slate appears on the south side of 

 Warren Street, a few rods west of Allston Street ; it is still 

 considerably contorted, but has a settled dip and strike, the 

 beds inclining to the north twenty to thirty degrees. These 

 three croppings of gray contorted slate probably belong to the 

 same bed ; but, if so, the one last described is separated from the 

 other two by a fault. 



North of this line of strike, and farther west, along the 

 south side of Warren Street, there are extensive ledges of grit 

 and sandstone, with pebbly layers at the base, and passing to 

 slate at the top ; the dip is northerly twenty to thirty degrees. 

 Immediately north of these ledges Warren Street appears to be 

 underlaid by amygdaloid ; but on the north side of the street 

 the sandstone, distinctly ripple-marked, dips N. 10° W. 30°. 

 On the east this is underlaid by amygdaloid, and indurated 

 near the contact ; and a little farther east it is apparently over- 

 laid by, but cannot be seen in contact with, a contorted and 

 rippled gray slate, which crops at two points along the strike, 

 and dips N. 10° W. 25°-35°. A little south of this gray 

 slate, and yet farther east, is amygdaloid, overlaid on the north 

 by a brownish-red, arenaceous slate striped with green, dipping 

 N. 20°-30°, and thoroughly indurated near the amygdaloid, 

 the contact showing clearly the intrusive nature of the last- 

 named rock. This brownish slate probably passes on the west 

 between the gray slate and the sandstone ; its geographic posi- 

 tion shows this ; and, besides, about ten rods farther north 

 there is another ledge of amygdaloid, overlaid on the north, 

 again, by a brownish-red slate precisely similar to the last, but 

 passing upward into the homogeneous gray slate, which is very 

 thin-bedded and dips N. 25°-30°. As before, the slate is 

 well baked near the amygdaloid ; the contact is extremely 

 irregular, typically igneous, though showing at the same time 

 much faulting. A study of these patches of sandstone and 



