TULLY LIMESTONE. 167 



it descends, and entirely disappears below the surface of the lake a few yards to the south 

 of Bloom's lime-kiln. 



In the Report of 1839, the facts here presented, namely, an elevation far above the lake 

 north of the county line, a depression bringing the lower surface of the limestone within about 

 a foot of the lake south of the line, then a rise of sixty feet, and subsequently a total disap- 

 pearance of it, appeared to be the result of an enormous curving of the rock, and not, as it 

 really is, an apparent curvature merely, caused by a change in the direction of the lake to 

 the southeast, the dip of the rock being to the southwest. Where the lake changes its direc- 

 tion below the county line of Tompkins, is the point where the rock descends from the north 

 and rises to the south ; and where it finally disappears, the lake returns to its usual or general 

 direction. That such is the fact is certain, from the accordance between the phenomena and 

 that of a plane surface whose edge corresponds with the outline of the lake along the range of 

 the TuUy limestone, when placed so as to accord with the dip and direction of that rock. 

 Thus if the plane be placed upon the map, spread upon a table, and raised so as to be in 

 contact with the map at the point which corresponds with Bloom's ferry, a dip to the south- 

 west being given to it, the point of greatest depression will be north of Goodwin's point, and 

 it will be raised at Ludlowville, and to the north also of the depression. The parallel of Lud- 

 lowville is four and a half miles east of Goodwin's point, near which the rock almost touches 

 the lake, and Bloom's kiln is five and a half miles east of that point ; a difference fully suflBi- 

 cient to account for an apparent curvature, which the experiment also satisfactorily explains. 



The Tully hmestone exhibits the same characters along the lake, as further east. It is 

 from eleven to sixteen feet thick ; color blackish blue and brown. One of the lower layers is 

 generally thick ; the bottom layer is frequently five feet in thickness. It is owing to this cir- 

 cumstance, and the softness of the shale beneath, that wherever a fall exists, the shale has 

 been washed away to some depth, leaving a chamber or cavern, the limestone forming the 

 roof or ceiling, as at the falls at Ludlowville, King's gully, and probably the Devil's den hke- 

 wise. 



This limestone often shows an accretionary structure, and a rough notched appearance 

 where its layers separate, as in some of the layers of the water-Ume group ; also the fibrous 

 appearance which belongs to epsom salts. 



Blocks of this limestone are very common along the lake shore, where the ledge is seen ; 

 requiring but to be encased with ice, the water of the lake raised, and then transported south 

 and deposited, to account for the blocks of the same limestone which there exist and are burnt 

 for lime, one of which is so large and so much buried as to appear to be in its original place, 

 and was supposed to be the projecting part of a ledge of limestone rock. These transported 

 blocks are found at various levels, to the south and east of Ithaca. In the latter direction, 

 near the road which leads over to Dryden, in one of the transported blocks, the Calymene 

 marginalis was found, which was described in the Report of 1839. The blocks which there 

 occur are at the height of several hundred feet above the lake, and in every probability formed 

 a part of the surface outcrop north of the line of the town of Genoa, and were transported 

 south over the hills when submerged. 



