RHODE ISLAND COAL MEASUEES. 179 



usually marked by minute slickensides or the appearance of a '^ grain" 

 running up and down the dip in the direction of the shearing movement. A 

 slickensided fault plane in the bedding is shown at this locality. 



Attieboro synchne. — Que of the few poluts ill tlio basin where the struc- 

 ture and superposition of beds are exhibited within a small area and in a 

 satisfactory manner is midway between Attieboro and South Attieboro, in 

 the elevation known as Ides Hill, lying between the Tenmile River and 

 Fourmile Brook. In this area of not over 2 square miles there is a well- 

 defined syncline in the Carboniferous strata, involving in the axis a thick 

 section of coarse compound conglomerates, immediately overlying the 

 highest of the rocks just described as lying north of the Perrins anticline. 

 The nose of this syncline is formed by the conglomerate, which stands up 

 as a low bluff at the crossroads IJ miles southwest from the station in 

 Attieboro. (See PI. XII.) The beds on the south side are vertical, and 

 can be traced along the entire area above described. The corresponding 

 strata on the northern side of the syncline are not so well exhibited. Near 

 the crossroads just mentioned, conglomerates exhibit a southward dip of 

 about 45^, and about 2 miles west, near Fourmile Brook, steep southerly 

 dips are again seen in conglomerate. Northward to the edge of the Wam- 

 sutta series the structure is not exposed. 



It seems probable that this group of conglomerates belongs on the 

 horizon of the Dighton group, at the top of the Goal Measures in this basin 

 (see p. 184), the red rocks of the Wamsutta group on the north having been 

 brought up against these higher beds by dislocation. 



Eastward of Attieboro and northward to the limits of the Providence 

 quadrangle in the directions named, the surface is too thickly covered with 

 glacial drift to make an interpretation of the under geology possible. The 

 area is, I confidently believe, underlain by Carboniferous strata, abundant 

 fragments of grayish conglomerates, grits, and sandstones occurring in the 

 drift. Judging from these erratics, which have not traveled far, con- 

 glomerates and the finer-grained rocks occur in this tract. The red Wam- 

 sutta beds may also be expected to reappear in this eastern area, folded in 

 with the gray rocks. Bowlders of this formation appear in the glacial drift 

 northeast of Attieboro. 



Westward of the line of section above described there are two or three 

 well-marked knobs of sandstone and conglomerate on the east of the road 



