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NEW YORK STATE MUSEUM 



the valley sides; and clay and sand plaiDS formed in the deeper 

 portions of these lakes. Subsequent erosion has done much to 

 modify the original features. 



From the rock formations and the overlying drift are obtained 

 stone, lime, gypsum, sand and gravel, clay and peat. In Living- 

 ston county, y 2 mile south of the Monroe county border, is an ex- 

 tensive deposit of marl which is used in the manufacture of 

 cement. Though there are in Monroe county smaller deposits 

 of this material, no attempt has been made to utilize them. 



Beginning at Lake Ontario, the first hard rock exposed is the 

 Medina sandstone. It underlies a belt of country averaging 

 about 5 miles in breadth and has a total exposed thickness along 

 the Genesee river of about 150 feet. In the basal 100 feet it is 

 a red shale or clay with some benches of argillaceous sand- 

 stone. The shale rapidly disintegrates on exposure and is suit- 

 able for brick manufacture. In the upper 50 feet or more the 

 formation is a red sandstone with shale partings, the less argil- 

 laceous parts being suitable for building purposes. This sand- 

 stone is developed on a small scale at various places along its 

 outcrop. 



The next formation is the Clinton, which underlies a belt of 

 country averaging iy 2 miles in breadth. It consists of two shales 

 and two limestones, aggregating nearly 80 feet in thickness. 

 The shales alternate with the limestones, the group beginning with 

 a shale. The shales have never been used, but experiments show 

 that they could be utilized in making brick. The lower limestone, 

 20 feet thick, is a thin layered, silicious limestone w T ith shale part- 

 ings. At one time it was quite extensively quarried along the 

 Genesee. The upper is a thin layered limestone lSy 2 feet thick, 

 with shale partings. Though it disintegrates rapidly on exposure, 

 it also has been quarried to some extent along the Genesee. 



Above the Clinton is the Rochester shale, forming a belt 

 averaging about 1% miles in breadth. It is a calcareous shale 

 or very impure muddy limestone, about 80 feet in thickness. 



On this rests the Lockport dolomite (limestone) underlying an 

 area about 4 miles in breadth. It has a thickness in the neighbor- 

 hood of 100 feet. It varies somewhat in its character, but may be 

 described as a magnesian limestone of drab color. It furnishes 



