LIME AND CEMENT INDUSTRIES 797 



at Rochester. ISTo analyses of it are available, but it is thin and 

 unimportant. 



The LoAver Helderberg limestone occurs sparingly along the 

 southern edge of the county, but is not quarried. 



The Quaternary marls and tufas are of some importance in 

 the county. The tufa is at times sufficiently extensive to be 

 used for burning into lime, and it is also massive enough for 

 structural work, a church having been constructed of it at Mum- 

 ford. 



Marl occurs at several localities in the county. Perhaps the 

 largest area is that along Aliens creek near Wheatland, this bed 

 extending into Livingston county. At some points the marl is 

 overlain by calcareous tufa to a depth of 3-4 feet. HalP gives 

 the length of the marl swamp as 3 miles, and its breadth as from 

 half a mile to 1 mile. At Mumford the tufa is well exposed in 

 a cedar swamp on the farm of Oliver Allen, ^ mile east of Mum- 

 ford station. It contains stems and leaves of cedar (pi. 49). Its 

 composition is as follows: 



Silica .5 



Alumina ) ^ 



Ferric oxid ) 



Lime carbonate 94.1 



Magnesium carbonate 2.3 



Insoluble .5 



99.4 



Under the tufa is a bed of marl. On the property of Mr 

 Ward, a florist in Mumford, tufa was encountered in sinking a 

 well, but at this point it was underlain bj blue clay. Marl also 

 underlies the cemetery at Mumford. 



According to Prof. Hall, another extensive deposit of marl 

 occurs along Mill creek, beginning at its source, and extending 



» Geol. 4th dist. N. Y. p. 429. 



