354 GEOLOGY OF THE NAKRAGANSETT BASIN. 



coal beds lie between 3,000 and 3,500 feet beneath the coarse conglomerate, 

 while the eastern bed lies between 500 and 570 feet beneath the conglom- 

 erate, so that eastern and western coal beds do not belong to the same hori- 

 zon, but one underlies the other about 2,500 to 2,900 feet, It should be 

 remembered, however, that these estimates are made without a knowl- 

 edge of the results obtained by a series of diamond-drill borings made west 

 of the eastern mine within recent years. The apparent failure to detect on 

 the western side of the syncline the coal bed which was worked in the 

 eastern mine also suggests either that the bed thins out westward or that 

 it has so far not been discovered on that side of the syncline. 



LTTHOLOGICAL variations in the shale series. 



The appearance of frequent sandstone beds and an occasional con- 

 glomerate layer on the eastern shore, east of the Portsmouth syncline, and 

 the exposure of only one or two coarse sandstone beds on the western side 

 of the syncline, on the brow of the hill east of Coggeshall Point and 

 northward (according to preceding calculations approximately at the same 

 level), suggests that there may be a reduction to the westward of the 

 amount of sandy material at this particular horizon. In a general way 

 also there appears to be more carbonaceous material in the shale series on 

 the east side of the Island of Aquidneck than at corresponding heights 

 westward, and there is certainly less carbonaceous material in the shale on 

 Prudence Island and on Bristol Neck than eastward. Observations of this 

 nature have little value, however, since the recorded strikes and dips are 

 not sufficient in number to give assurance regarding the strike and dip of 

 the intermediate localities, where exposures fail or where the stratification 

 has been obscured by cleavage. 



GEOLOGICAL STRUCTURE OF THE MIDDLE THIRD OF AQUIDNECK 



ISLAND. 



From McCurrys Point to the exposures half a mile north of Black 

 Point, little can be determined about the dip of the rocks. In the Grlen a 

 sandstone layer appears to be nearly horizontal. Nothing satisfactory could 

 be determined about the dip of the exposures along the road from Slate 

 Hill southwestward. North and south of Lawtons Valley, and at several 



