Luther — Geology of the Salt District. 



201 



appears in this state west of the central part of Oswego county. The 

 sandstones are of more frequent occurrence and much heavier in the upper 

 part of tin; formation, and in many localities are crowded with fossils. 



The Hudson river slate and sandstones are the surface rocks of a large 

 area in the northern and eastern part of Oswego county and of Jefferson, 

 Lewis and Oneida counties and crop out along the south side of the Mohawk 

 valley in Herkimer and Montgomery counties. 



The upper beds thin out toward the east and dissappear before reaching 

 Salt Springville, and the brine springs, found here and previously mentioned 

 as being the lowest in the strata in the state, issue from the upper part of the 

 softer lower division of the group, -which is here in direct contact with the 

 rocks of the overlying Medina formation. 



It is exceedingly difficult to determine in a well boring just when the 

 limits of this group are passed, and hence its thickness in this region has been 

 accurately fixed in but few places. 



In a deep well at Utica, the thickness of the Utica and Hudson river 

 slates and sandstones aggregated 800 feet. Inone at Fulton, Oswego county, 

 as found by AValcott, 1000 feet ; in one at Wolcott, Wayne county, reported 

 by Prosser, 1080 feet, and in the one at Rochester, according to Fairehild, 

 598 feet. 



Oneida conglomerate. Next in the order of superposition there occurs in 

 the eastern part of the district under consideration, a bed of coarse red and 

 white sandstone in which are embedded roundish pink and white quartz pebbles 

 in great numbers. This is the Oneida conglomerate. It is best developed in 

 Oneida county, where it attains a thickness of 100 feet or more'. It thins out 

 rapidly toward the east, disappearing under the drift in Herkimer county, to 

 reappear in the Shawangunk mountains where it has received the local name 

 of Shawangunk grit. It also thins out, or loses its pebbly character in the 

 western part of Oswego county, whence westward on the shores of lake 

 Ontario the lowest surface rocks belong to the division of the Medina group 

 known as the Medina sandstones. 



Medina sandstone. These rocks are not all sandstones but include many 

 beds of shale. Red is the predominating color in both sandstones and shales, 

 but the former are sometimes white, grey, or mottled, and the latter frequently 

 bluish or olive. 



Professor Hall recognized the following subdivisions of the Medina sand- 

 stone beds: At the base, (1) greenish grey sandstones with no distinct line 



