RHODE ISLAND COAL MEASURES. 177 



iting a clear instance of local erosion following the deposition of red shales 

 and preceding the deposition of more gray beds. Angular fragments of 

 the red shale occur in the overlying gray beds, completing the evidence of 

 unconformity at this point. The structure is indicated in the accompanying 

 diagram of the locality (fig. 24). 



A few feet stratigraphically below this level of contemporaneous 

 erosion and a few yards westward in the vertical beds is the well-marked 

 unconformity before mentioned. It is partly concealed by glacial gravels, 

 but shows the cutting off on the west of about 20 feet of fine sandstones. 

 The continuation of these beds on the west of this ancient channel of 

 erosion is not exposed. The excavation or channel thus formed was subse- 

 quently filled with coarse sands, which also mantle over the fine sandstones 

 to the eastward of the ancient stream bank. 



The phenomena of this horizon indicate clearly the fiuviatile nature 

 of the sedimentation in this portion of the Carboniferous area, The deposits 

 may have accumulated near sea level, but under conditions in which the 

 streams were given steep gradients and large supplies of freshly eroded 

 detritus of granite and quartzite, as if in some mountainous lake or bhabar 

 district, such as that at the southern base of the Himalayas in India. 



Red shales. — The red shales which now succeed the gray beds can be 

 traced southwestward along the southern side of the Attleboro syncline. 

 They alternate with gray sandstones, and where most distinctly shown have 

 an ascertained thickness of 60 feet. Strata which exhibit a reddish color, 

 however, continue upward in the section nearly to the base of the coarse 

 conglomerate which forms the nose of the syncline. On the land of Mr. 

 Joseph Fisher the following section is exposed : 



Section near Attleboro, on Thatcher road. 



Feet. 



Red shales and sandstones with gray sandstone interlaminated (top not seen) 22 



Sandstone, gray ! 8 



Sandstones, grayish-green (quarried) 52 



The red sandstones contain annelid borings. 



A little higher up than these red strata is a coarse conglomerate. Still 



higher up are fine conglomerates with pebbles of quartzite, granitite, and 



quartz. (See PL VIII.) The quartz is often deeply stained with iron oxide. 



Overlying these fine conglomerates are the reddish-tinged strata mentioned 



mon xxxiii 12 



