154 GEOLOGY OF THE THmD DISTRICT. 



and turning round by the northeast, being the only part of Nelson which contains the group 

 as surface rocks. It extends into De Ruyler from Cazenovia, diminishes in width, and enters 

 the northeast end of Cortland firom De Ruyler in a narrow strip. 



In Onondaga county, it covers the greater portion of the town of Pompey, the north end 

 only having other rocks. It covers the whole of Lafayette except the northeast end, the 

 whole of Otisco, the greater part of Onondaga, the lower half of Marcellus, and all of Ska- 

 neateles but the northern portion. It forms llie greater part of Fabius and Tully, and a part 

 of Spafford. There are a few exceptions to be made in this county, such as the Tully lime- 

 stone in Pompey, Otisco and a few other localities, which in a practical point of view are of 

 httle consequence, as this limestone covers but small areas. 



In Cayuga county, the group covers the greater part of Owasco, the northern portion of 

 Sempronius, the largest portion of Fleming, the northern and eastern part of Scipio, the 

 southeast half of Springport, the greater part of all Ledyard, extending thence along the lake 

 to the county line. From the great deplli of the valley at the head of Owasco lake, the group 

 ai^ars in the side-hills to tlie south of Moravia. 



No part of the group appears in Herkimer county, except in the town of Winfield ; and 

 in Oneida county, in the towns of Bridgewater and Sangerfield, extending into the southwest 

 part of Paris-lull, and the southeast part of Marshall, and also in the southern part of Augusta. 

 It terminates or caps the high hills or ridges which come up, as it were, firom the south. 



In Cortland county, it is but very partial, and is foimd only in the north part of Truxton. 



In Chenango county, it forms a strip along the Unadilla river, of about three miles wide 

 at the north line of the county, and terminates a few miles south of North New-Berlin. It 

 covers the larger northern half of Sherburne, and a portion of the northeast part of Smyrna. 



In Tompkins county, it is found only on Cayuga leike, being a strip which comes to an end 

 about three miles below Ludlowville. 



At present a few localities only will be mentioned of the shales and the more solid or harder 

 masses, reserving the detail for the counties, and to those where the group occurs ; first enu- 

 merating the different parts observed on Cayuga lake, some of which have not, however, been 

 recognized towards the east end of the district. 



The first rock going south on the lake, after passing the low clayey ground to the south of 

 Springport, may be considered as the dividing line between the Marcellus shales and the 

 Hamilton group. It is a dark slaty fossiliferous shale, with numerous individuals of the Orthis 

 umbonata of Mr. Conrad, but usually small, associated with the Limitary orthis (0. limitaris) 

 also numerous, etc. It shows about six feet of a brownish black impure limestone. This 

 part forms the small rise about half a mile or more below Levana. It appears in the road 

 from Springport to Levana, at Crise's brook ; on the road to Auburn from Springport, two 

 miles southwest of Half-acre ; to the northeast of Skaneateles on the road to Marcellus, and 

 on the north side of Pompey hill, etc. The Umbonated orthis (O. umbonata), which occurs 

 in myriads in this part of the group in Cayuga county, was not noted as having been seen in 

 the same position at the east end of the district. 



