PRUDENCE ISLAND. 239 



found as at this level. The general strike is parallel to the shore, about 

 N. 10^ E, south of the wharf, and N. 3° to 6° E, farther south. The dip^ 

 which is 25° E. for the greater part of the shore exposure, becomes 40° E. 

 near the southern end. Here there is also much local crumpling, which 

 brings the color bands of the rocks often to a vertical position. The 

 crumpling takes place in a direction N. 60° E. 



South of the wharf the coaly shale often shows distinct color banding. 

 Gray, rather coarse sandstone occurs along the top of the cliff The shale 

 is frequently ottrelitic About 3,375 feet south of the wharf fossil ferns 

 were found in the coaly shales, where finest grained and least ottrelitic. 

 Ferns are difficult to find in this series. It is best to take each slab of shale 

 in the hand and hold it so that the sunlight will bring out in sharper relief 

 all the unevenness of the surface. When the fern-leaf impressions are once 

 found, the character is readily enough recognized. In the sandstone which 

 occurs in the coaly shale series at this point was found the impression of a 

 very large calamite. The longitudinal ribs were very coarse and distinct, 

 and although the specimen was about 14 inches long and 4| broad, yet it 

 showed not a single joint. 



The most northern exposure on the east side of the island occurs about 

 two-thirds of a mile north of the light-house at Sand Point Here is found 

 a rock belonging to the shale series, finely color-banded, very micaceous, 

 but not fissile. The strike is N. 12° W. and the dip 75° W. The next 

 exposure is hardly half a mile north of the light-house. It is very dark- 

 blue ottrelitic rock, belonging to the shale series. Its strike is about N. 

 4° W. and its dip about 80° W. From the south side of the light-house 

 southward for a distance of 1 J miles there is a continuous exposure of the 

 shale series along the shore, after which there are several more isolated 

 exposures for about a quarter of a mile farther. The rocks on this side 

 also belong to the shale series, although evidently higher than the basal 

 part of that series as exposed on the west shore, since neither the sand- 

 stone-conglomerate series below nor the lower black coaly shale layers are 

 here exposed. These shales usually appear so different from the Conanicut 

 shales that at first sight their close similarity might not be recognized, yet 

 careful observation will show at once the same sericitic micaceous structure. 

 The rock is usually rather firm, but frequently the shaly structure is more 

 developed and then the rock resembles in every particular the greenish and 



