r 



STRUCTURE, ATTITUDE, AND FOSSILS. 507 



promontory, appear the remaining beds of C — magnesian limestone inter- 

 stratified with sandstone. The ruins of the fort, 50 or 100 feet above the lake, 

 are on the mottled limestone at the base of B, containing Ophileta complanata, 

 Vanuxem, and a large Orthoceras. One hundred rods farther northwest, 

 the railroad tunnel is cut through the magnesian limestone of D, and above 

 the tunnel at the north end appears the banded sandstone of D. These and 

 the superjacent strata are best seen farther west on the steep southern slope 

 of the promontory, until finally, 40 rods southwest of the forks of the road, 

 we reach the drab limestone of division E, whose sudden change in dip 

 (N. 23° E.) and strike (N. 60° W.) indicates approach to some scene of 

 disturbance. Farther east, north of the main highway, there are other 

 exposures of the drab-colored limestone. These drab-colored limestones are 

 fossiliferous, carrying a form like Stenopora fibrosa, Goldfuss, Euomphalus, 

 aud uudescribed species of Orthoceras, Cyrtoeeras, and Lituites. 



Southeast Charlotte Section. — Twenty miles north of old Fort Ticonderoga, 

 at Thompson's point, is another remarkable display of nearly all the members 

 of the Lower Silurian. It is another monocline, dipping from 12° to 20° to 

 the southeast. It is especially interesting, for in division D occur the Fort 

 Cassin series of rocks and fossils. In E are found the Cove islands, which 

 offer forms of Primitia.* On the bluffs on the shore, also, undescribed 

 species of Primitia are found in the strata underlying the Chazy. 



Providence Island Section. — At Providence islaud, 24 miles north of 

 Thompson's point, there is an interesting exposure of the upper part of divis- 

 ion D and the lower part of division E of the Calciferous rock. The main 

 body of the island dips to the northeast, and successive beds are displayed 

 along the shore. Special points of iuterest connected with this section are 

 the occurrence of the Fort Cassin fossils in division D, represented by the 

 group Calaurops lituiformis, Whitf., Maclurea affinis, Bill., Lituites eatoni, 

 Whitf., Nautilus helloggi, Whitf., and the Shoreham fossils of E represented 

 by Murchisonia confusa, Whitf, Bucania triplet,, Whitf, Primitia seelyi, 

 Whitf., with undescribed gasteropods and cephalopods. The total thickness 

 of E, 450 to 500 feet, corresponds well with the thickness observed farther 

 south. 



The Fort Cassin Strata. 



In 1885 we found on the site of Fort Cassin, isolated on the peninsula at 

 the mouth of the Otter, a locality rich in a fauna chiefly new to science, 

 31 new species being distinguishable, with still others too poorly preserved 

 to be described with accuracy. This group then seemed to us more nearly 

 related to the forms we know in connection with the upper division of the 



* Bulletin Am. Mus. Nat. His., Vol. II, 1878-'0o, pp. 58-60. 



