CARBONIFEROUS LIMESTONE. 



119 



nodules, the upper, more limestone-like arenaceous beds of which 

 contain Zaphrentis spinulosa, Lithostrotion proliferum, Syringo- 

 pora ramulosa, and Productus Flemmingii. Above the arenaceous 

 beds are 6 or 8 feet of light-colored brittle limestones with an abun- 

 dance of flint nodules, interlaminated with thin seams of greenish 

 shales. The limestones contain, besides the fossils mentioned, 

 Fenestellas and other Bryozoa. In former years the limestone was 

 quarried there, but at present the place is abandoned. The Charity 

 Islands are composed of the same rock beds as Point Aux Grees. 

 On the largest of them, on which a lighthouse is built, the north- 

 east shore presents the best exposures. The bluffs are nowhere 

 over 8 feet high, being generally lower. One place exhibits a very 

 interesting example of discordant stratification. The lowest beds, 

 a light-colored, ripple-marked, calcareous sand rock, project in a 

 gentle arch about one foot above the water level, and from both 

 sides higher strata dip away from the convexity at a sharp angle, 

 resembling the anticlinal position of an uplift, with about 50 feet of 

 rock beds on each side of the arch, in an imbricated order, and hav- 

 ing at their projecting ends about the same level. The higher 

 ledges of this anticlinal series are still arenaceous, but the lime 

 prevails, and for them the name of lime rock is more appropriate 

 than that of sand rock. They contain flint concretions, Zaphrentis 

 spinulosa and Lithostrotion proliferum, and the surface of nearly 

 all of them is ripple-marked. Over the surface of this anticlinal 

 series, horizontal limestone ledges are deposited in obvious dis- 

 cordance with the subjacent ones. These upper ledges are a pure 

 lime rock, free of sand, but inclosing numerous flint nodules, and 

 interlaminated with thin seams of calcareous shale. Lithostrotion 

 ■proliferum, Syringopora ramulosa, Fenestella, Polypora, Productus 

 Flemmingii, Allorisma clavata, and Fish-teeth are the usual fossils, 

 but are not found in great abundance. The thickness of these upper 

 horizontal beds is about 8 feet. Higher strata are not observed 

 on the island ; its west side is low, marshy, and covered with loose 

 rock debris and sand. The subjoined sketch illustrates the irregu- 

 larity of stratification which I have just descrbed : 



