296 OEOLOGT OF THE THIRD DISTRICT. 



appear to accompany the particles of limestone in all the upper rocks, the carbonate of iron 

 being in considerable quantity at the upper part of the Catskill group, and under the coal 

 deposit in the neighborhood of Ralston in Lycoming county, Pennsylvania ; and it is there 

 worked, affording the purest of iron. 



14. Tompkins County. 



The east half of this county, embracing the towns of Lansing, Groton, Dryden, Caroline, 

 Danby and the east half of Ithaca, belong to the third district, tlie county being divided 

 between this and the fourth district. 



The lowest rocks of this portion of the county are those of the Hamilton group ; but they 

 are only to be met with along Cayuga lake, commencing at the north end of the county, and 

 continuing up the lake to near Bloom's lime-kiln, below which they disappear under the Tully 

 limestone and the lake. They are well exposed along the creek at Ludlowville, disappearing 

 also under the same rock at the falls in the creek, and the ravines near the village. 



The Tully limestone is the next rock in succession. It is also seen in the same range of 

 country, being well exposed along the lake, and readily traced from the county line to the 

 kiln, where it was quarried and burnt for Ume. Along the shore in many places are nume- 

 rous large blocks of the rock, which have fallen from the cliff, owing to the removal of the 

 soft shale beneath it upon which it rested. Blocks of this rock have been transported many 

 miles south of the head of the lake, along the high grounds of the Cayuta and Six-mile creeks, 

 and are quarried for lime ; also on the road to Dryden, three or more hundred feet above the 

 lake. 



The Genesee slate, the conunon associate of the limestone, also appears on the same side 

 of the county, ranging with the two lower masses, and showing a greater extent of surface, 

 as may be seen along Salmon creek ; and extending up the creek from the falls over the Tully 

 rock, as well as in some of its other branches, the south one for example, where it forms two 

 falls. 



Portage and Ithaca groups. These groups cover the remaining part of the town of Lansing 

 the whole of Groton, the northwest half of Dryden, and the southwest part of Ithaca. The 

 lowest layer along the lake is a hard solid sandstone of variable thickness, some parts about 

 four feet, being the maximum. They show at Falls creek, Cascadilla creek, the Inclined 

 plane, and at McCormick's quarry, some good building stone ; but the great mass consists of 

 rather hard and coarse shale, some quite slaty. Though the shale is somewhat enduring in 

 the mass, when the edges merely are exposed, as is obvious in the cliffs along the lake, and 

 at the falls of the creeks near Ithaca, the Inclined plane, etc., yet it is but a perishable mate- 

 rial when otherwise exposed. 



Chemung group. In the present state in which this group is placed, but Uttle need be said, 

 especially as it must occupy but a very small part of the east half of the county. Considering 

 it to commence towards the upper part of the Inclined plane, no change whatever was noticed 



