STEUCTTJEE OF AQUIDNECK SHALES. 355 



points along the western sliore, the dip, however, is distinctly eastward. 

 Over this more eastern part of the middle third of Aquidneck Island the 

 strata are believed to be inclined at a low angle, and to form a series of 

 low folds, leaving the rocks in general essentially horizontal. Along the 

 western coast, however, and for a distance of a mile or more east of the same, 

 more marked eastward dips occasionally occur, and here the folding may 

 be more pronounced, although the recorded observations so far fail to give 

 evidence of marked folding. 



STRATA PROBABLY FOLDED. 



If the coarse conglomerates of Coddington Point, Coasters Harbor 

 Island, and Miantononiy Hill correspond to the coarse conglomerates in the 

 northern third of the island, it is evident that, in spite of the eastward dips 

 so far recorded from the western Portsmouth mine as far as Coddington 

 Point, there must be some system of folding as yet not discovered, which 

 (1) allows the Miantonomy Hill exposure of conglomerate to appear to the 

 west of the line of strikes shown by the shales to the northward, while they 

 are still evidently above the Aquidneck shales as exposed near the hill; (2) 

 the fact that the Coasters Harbor Island and the Coddington Point expo- 

 sures of coarse conglomerate lie at least 100 feet beneath those at Mianton- 

 oniy Hill suggests that there must be folding between these localities, if 

 the two sets of coarse conglomerates are to be considered as of the same 

 age, and the exposures at Coasters Harbor Island and Miantonomy Hill 

 favor that view. 



The synclinal structure of the southern half of Prudence Island and 

 the northern third of Aquidneck Island demands anticlinal structure in the 

 region between. How far south either the anticline along the Eastern 

 Passage or the syncline of Prudence Island extended is unknown. Are the 

 coal beds in the western mines near the base of the Aquidneck shale series I 

 Do these coals thin out westward? Are the coaly shales on the western 

 shore of Prudence Island the representatives, in a general way, of the 

 thicker coal beds at the Portsmouth mine '. Do the coaly shales of Grould 

 Island belong to the same horizon — i. e., that of the Portsmouth mine coal 

 beds? These are questions which can not be satisfactorily answered in the 

 present state of our knowledge. 



