118 PROCEEDINGS OF THE BOSTON MEETING 



because of tbe gentle southerly dip of the strata. The block diagram, figure 1, 

 illustrates how this would occur. 



The Field Evidence 



The New York State geologic map of 1901 shows the Niagara limestone es- 

 carpment jogged northward in the manner of figure 1 for a distance of about 

 three miles, at Clarendon and Holley, Orleans County, New York, and the 

 Onondaga ( Cornif erous ) scarp similarly affected two miles east of Batavia,^ 

 where crossed by the New York Central main line. These two offsets (see 

 map, figure 2) are in line with each other and with a discordance of the 

 stratigraphy at Linden and the valley of Dale, Wyoming County, New York, 

 recognized by the writer in 1918. 



The relations at Linden are as follows : The strata involved are the Upper 

 Devonian (Portage and Genesee) formations, whose thicknesses^ are approxi- 

 mately : 



Feet 



Nunda sandstone 150 



Gardeau shales and flags 300 (285) 



Hatch shales 150 (125) 



Rhinestreet black shale 90 (60) 



Cashaqua olive shale 80 



Middlesex black shale 20 



West River dark shale 30 



Genundewa limestone 1 



Geneseo ^ black shale 25 



The total thickness between the Nunda sandstone and the Genundewa lime- 

 stone is, therefore, 670 (600) feet. The falls at Linden are over Geneseo 

 shale capped by Genundewa limestone (1060 contour), each with character- 

 istic fossils; but in the ravine a mile west the base of the Gardeau beds is 

 found at only 1,264 feet above tide resting on the darker Hatch shales, and the 

 Nunda sandstone appears at only 1,490 feet in the road north from Vernal, 

 seven-eighths mile southwest from the preceding. These figures, which 

 check with other outcrops, harmonize with the proper thickness of the Gar- 

 deau, but demand either an excessive drop or a remarkable thinning of the 

 strata in the first mile west of Linden. The discrepancy is not less than 

 100 feet. 



That there is really an abrupt drop here is demonstrated three miles south 

 up the same valley (locally "the dale"). On the west side of this valley, 

 a mile and a half north of Dale, the Nunda sandstone at 1,385 feet above 

 tide caps a 200-foot cascade, which exposes only the Gardeau down to the 

 mouth of the ravine. Directly across the dale, on the east side, the dark 



' Compai-e the corresponding jogs in the Albion moraine and the Warren beaches on 

 Leverett's map, pi. iii, Mon. xli, U. S. Geol. Survey, pp. 702, 768-9. 



*Luther : Bull. 172, N. Y. State Museum. See under each formation. 



s The name "Genesee" is in duplicate use for the group (including the West River) 

 and for the part beneath the Genundewa limestone, which is under water at Hall's type 

 locality. To avoid confusion, the variant Geneseo may be given to the latter, which is 

 84 feet thick in the fall on Fall Brook, Geneseo, N. Y. 



