776 NEW YOEK STATE MUSEUM 



cement manufacture^ as tlie lowlands which the limestone ledges 

 border are underlain by clay. The Chazv limestone bears a hich 

 reputation not only for the manuifacture of lime^ but also as a 

 furnace flux. 



The following is an analysis of the burned stone used for flux 

 at Troy, E. Touceda, analyst. 



Lime oxid . 97 . 48 



Magnesium oxid 1.4 



Alumina 14 



Ferric oxid 12 



Silica 79 



Total 99 . 53 



Columbia county^ 



The limestones in the eastern part of the county are of little 

 importance on account of their impure nature, but on Becraft 

 mountain east of Hudson the stone has been extensively quarried 

 for a number of years to supply the "furnaces at Troy with flux. 

 Two types of stone are found here, viz the Becraft or Scutella 

 limestone, and the blue Pentamerus rock. 



The Pentamerus limestone is quarried on the cemetery prop- 

 erty at the northeastern edge of the town (pi. 32). It is well ex- 

 posed in a face about 100 feet long and 25 feet high. With the 

 exception of the upper 6 feet the layers are quite free from chert. 

 The rock shows occasional cavities with calcite crystals and at 

 times quartz, but otherwise probably does not run over S/^ or 4^ in 

 silica. While the stone has hitherto been used only for road 

 material, still it affords a source of limestone for the manufacture 

 of Portland cement, the necessary clay being obtainable from the 

 terraces north of the city. 



The most abundant material is the Becraft limestone already 

 roferred to. Extending along the top of the ridge are a series of 



1 Bishop, I, P. On certain fossiliferous limestones of Columbia county 

 iSr. Y. and their relations to the Hudson river shales and the Taeonic system. 

 {see Am. jour. sci. 1886. 32: 438). 



Mather, W. W. Geol. 1st dist. N. Y. 1843. 



