24 NEW YORK STATE MUSEUM 



In tracing the beds farther east, the gypsum disappears as a 

 promiment feature, but the top of the SaHna is found at about 900 

 feet at CUnton, Oneida co. and between 1400 and 1500 feet in Her- 

 kimer county. Beyond Herkimer county the elevation drops off 

 rather rapidly so that in Schoharie county the single member of the 

 series outcrops at about 600 feet. 



The lowest point of outcrop is nearly on line with Cayuga lake 

 where the belt is widest. There is a rise of about 300 feet between 

 that point and Genesee county and of over 1000 feet in the interval 

 between Cayuga lake and southern Herkimer county. The main 

 part of the belt has thus the structure of a broad shallow syncline 

 with an axis running north and south and with its eastern wing 

 rising well above the western. 



Nature of the gypsum deposits 



The gypsum forms regularly stratified beds which are usually 

 heavy and range from several inches to 5 feet or so thick. The 

 impure argillaceous gypsum is, however, rather thinly bedded, the in- 

 dividual layers being separated by shale intercalations. The strata are 

 not, of course, absolutely continuous along the Salina belt, but have 

 the shape of elongated lenses which succeed each other along the 

 strike and dip, perhaps after intervals occupied only by the accom- 

 panying shale and hmestone. The workable deposits are thus sepa- 

 rated into more or less well defined areas, on the borders of which 

 the gypsum diminishes or entirely disappears. 



The lenticular form of the deposits is well illustrated by the area 

 near Akron which has been fairly well dehmited by exploration 

 underground and by numerous test holes [see map facing p. 50]. 

 The bed averages about 4 feet thick and extends for nearly 2 miles 

 in an east-west direction before it thins out. On the north or out- 

 crop side it apparently diminishes very slightly and then terminates 

 abruptly, a feature which is due probably to removal of the gypsum 

 by erosion. The extension of the bed on the dip has not been thor- 

 oughly explored, though the available evidences indicate a gradual 

 thinning in that direction. 



In surface exposures the beds may exhibit local modifications of 

 the lenticular form. Several occurrences illustrative of such irregu- 

 larities have been described and sketched by Hall^ with considerable 

 detail. Two of his sketches are reproduced herewith [fig. 3, 4]. 

 In explanation of the features shown in figure 4, Hall expresses the 



1 Survey of the Fourth Geological District. 1843. p. 119 et seq. 



