THE AQUIDNECK SHALES. 349 



SOUTHERN CONANICUT. 



The shales on Conanicut form a singularly uniform series. Owing to 

 abundant cleavage, they are everywhere strongly fissile, sj^litting into thin 

 plates. The color is usually dark blue, appearing nearly black where 

 moistened by water, and more brownish or greenish brown where very dry. 

 But variations from greenish to nearly black occur also, entirely aside from 

 any question of moisture, the darkening of color being due to the amount 

 of carbonaceous material present. This gives rise to an alternation of 

 darker and lighter color bands, which is very characteristic of the shales in 

 many parts of Conanicut, and without which it would rarely be possible to 

 determine the plane of stratification of the rock. Not a trace of conglomerate 

 or of coarse sandstone has so far been found in the shale series of Conanicut. 

 Thin layers of a very fine-grained whitish sandstone occur along the 

 southern margin of Dutch Island Harbor, along the shore east of Fox Hill, 

 and on the eastern shore along Freebodys Hill. Where there is no color- 

 banding- or whitish sandstone there is no means of learniug the real dip 

 and strike of the shales, the cleavage obscuring all traces of stratification. 

 The dips on the western side of Conanicut are certainly, in places, very 

 steep to the westward, practically vertical, but at the first exposure south of 

 Fox Hill the dip is between 45° and 60° E., and this, in connection with 

 the general eastward dip of the strata on Fox Hill, is one of the main 

 reasons for believing that the Aquidneck shales overlie the Saunderstown 

 sandstones. 



On the eastern side of the western division of the island — i. e., along 

 the western side of Mackerel Cove and thence southward — the dips are 

 usually eastward at angles which are frequently as low as 45°, and some- 

 times much lower. On the eastern side of Mackerel Cove the dip is low to 

 the east. On Freebodys Hill some of the dips are nearly horizontal, others 

 are low to the east, and in places the dip is very variable. So little being 

 known of the geological structure of the island, it is impossible to form a 

 close estimate of the thickness of the shale series exposed there. A mini- 

 mum estimate would be 2,000 feet, while 4,200 feet can not be called a 

 maximum for the entire series, considering the steep dips on the western 

 side of the island. The coaly shales on Fox Hill, at Beaver Head, may be 

 considered as forming a transition series between the Kingstown sandstones 

 beneath and the Aquidneck shales above. 



