EHODE ISLAND GOAL MEASURES. 193 



The extension along their strikes of the several strata thus obscurely 

 exposed can not be traced with certainty more than a few rods. As in the 

 Mansfield area, there are no indications of the higher beds of the Carbonif- 

 erous section, so well exposed in the deep synclines of Dighton and Taun- 

 ton. The beds for the most part appear to belong to the few hundred feet 

 of Coal Measures coming in above the red Wamsutta series. Unless the 

 Carboniferous formation thinned out in this direction, the post-Carbonifer- 

 ous erosion of beds of this age alone in this field must be measured as 

 upward of 10,000 feet of strata. 



ABINGTON QUADRANGLE. 



In the southern part of this quadrangle more has not been possible 

 than roughly to discriminate the lower reddish strata of the Wamsutta 

 extension from the area occupied by the gray Carboniferous strata of the 

 Coal Measures. The first-named series has already been described on 

 page 143. 



There are about a dozen exposures of the gray series of the Coal 

 Measures known in this quadrangle. Beginning on the northwest, in 

 Abington, the gray series is seen in a small outcrop about 1J miles south 

 from the granitite border. It is over 5 miles from this locality southward to 

 the outcrops including Sachems Rock near the Satucket River, in the town 

 of East Bridgewater. 



Sachems Rock is a knob about 175 feet long and 20 feet high, composed 

 of massive-bedded, somewhat altered sandstone with bands of small pebbles 

 of white and smoky quartz, a fine-grained granitic rock, and a slate of 

 undetermined origin. The attitude of the beds is nearly horizontal, dipping, 

 if at all, to the north. There is a pronounced cleavage striking N. 77 °W. 

 The western side of the ledge has been opened for the purpose of quarry- 

 ing. The smaller exposures to the east along the street are like the first, 

 showing to the eye abundant minute scales of muscovite. The cleavage 

 planes maintain the same direction, and dip steeply to the north. 



These beds are on the southern side of the broad, shallow syncline 

 which covers the southern part of the Dedham area, next north. They 

 would come, in accordance with the supposed structure, low down in the 

 Coal Measures. 



In Hanover, half a mile east of Drinkwater River, and about 2,100 

 mon xxxiii 13 



