104 Eepoet of the State Geologist. 



the Tully ; in which I must concur with him. The leading facts 

 in the case of the Tully are these : 



From the most northern exposure the Tully descends 400 feet 

 in four miles, into Seneca lake ; then runs four and one-half miles 

 practically on a level ; i. e., with two bends of 50 feet, ending at 

 the lake level again, brom the northern exposure to a point near 

 Cayuga lake equivalent in altitude to Seneca, brings us to the creeks 

 just south of Kidder's Landing, two miles farther south than the 

 foot of the western dip. It is nearly level for three miles south of 

 this. A line connecting these points runs about W. 15° N., and 

 may be taken as the axis' of the fold. A line drawn from the 

 northern exposure vertical to this line would be three miles long, 

 which would give a dip of ^^ =133 feet to the mile, at this 

 point, succeeded southerly by nearly hoiizontal strata for a few 

 miles The important anticlinal south of Truman sburg does not 

 affect the county. 



Subordinate in magnitude, but confirmatory, is the dip of the 

 Hamilton in the western part of Fayette and Yarick. The single 

 exposure of the base of the Hamilton, in the form of a coral bed 

 or reef on the summit of a hill, 2 00 feet above Seneca lake, is 

 rediscovered at the lake level four miles S. lo° W.; and at two 

 and one- half miles, perhaps 25 feet above the lake in Reeder's 

 creek. The latter corresponds to a dip of 70 feet per mile. 



The general average of thickness for the Hamilton group maybe 

 taken between West Fayette station (608 A T.) and Willard quarry, 

 eight and one-half miles due south (555 A. T ). Allowing 53 

 feet in addition to l,14i (Ithaca well), we have, in round num- 

 bers, if^^ = 141 feet dip to the mile. Using Hall's estimate we 

 have if^^ = 1'23. Measurement along the supposed axis of dip 

 N. 15° E , does not materially alter the result. 



It is evident that the dip of the Marcellus and the Upper Hel- 

 derberg is at a very different angle from the above, unless our 

 estimates of their thickness are altogether wrong. It is uncer- 

 tain where their upper limit lies. There is a distance of 8 -f miles 

 between known exposures, from Waterloo to bluffs north of 

 Eeeder's creek, on the same level. On a N-S line 10 miles is not 

 improbable, giving ^-^^ = 16 feet of dip per mile. 



It is easy to play with figures ; but perhaps the fairest average 

 tate ment is the following, which is based on exposures at the 



