54 



NEW YORK STATE MUSEUM 



UNDULATIONS OF THE STRATA 



The aggregate thickness of the geologic formations and parts of 

 formations represented on the map of the Penn Yan and Ham- 

 mondsport quadrangles is approximately 2187 feet, of which 1535 

 feet are surface rocks by reason of the difference in elevation be- 

 tween the point where the east line of the Penn Yan quadrangle 

 crosses Keuka outlet 525 feet A. T. and the extreme southeast cor- 

 ner of the Hammondsport quadrangle which is 2065 feet A. T. 

 The total amount of the southward dip in the 34 miles across the 

 two quadrangles from north to south is about 652 feet, an average 

 of a fraction less than 20 feet a mile. 



The inclination of the strata is not constant in any direction ex- 

 cept for short distances, and there are evidences of more or less 

 disturbance throughout the whole of the area covered by the map. 



The sandstones of the beds that cover the southern part of the 

 Hammondsport quadrangle are not reliable as bases for accurate 

 determination of the size, shape and direction of the folds and un- 

 dulations except in a general way. In the rock cut along the 

 Northern Central Railroad 2% miles southeast of Penn Yan a com- 

 pact sandstone 2 feet thick is exposed that is probably synchronous 

 but not continuous with a stratum of similar character that appears 

 at the mouth of Watkins Glen and the one assumed as the base of 

 the Portage beds at Ithaca. 



In this cut the sandstone shows a strong dip toward the west, but 

 at the west end it is 840 feet A. T. and in the Sartwell gully 2 miles 

 farther west it appears at 880 feet A. T., 40 feet higher. It de- 

 scends between this point and the quarry in the Cornwall ravine, 

 miles northwest, 35 feet and in the quarry dips northwestward at 

 the rate of 52 feet a mile. 



The Tully limestone, from its outcrop at Seneca Mills, dips south- 

 eastward to Plum point on Seneca lake at the average rate of 26 

 feet a mile and rises toward the north to Bellona at the rate of 16 

 feet a mile. Estimates based on other outcrops of the Tully 1 mile 

 east of that at Seneca Mills, where there is evidence of a con- 

 siderable fault or very sharp fold, would give altogether different 

 results. 



The strata show more disturbance in the region about Penn Yan 

 than elsewhere on these quadrangles, and small anticlines or down- 

 thrusts may be seen in nearly every ravine or outcrop in the vicinity. 

 W In a ravine on the west side of the lake 3 miles southwest from 

 Penn Yan at about 100 feet above the lake, a 4 foot sandstone that 

 crosses the ravine is much broken and shows a diagonal fault or 



