GEOLOGY AND PALEONTOLOGY OP THE SCHOHARIE VALLEY 355 



of which is a revolving shaft carrying a wooden frame with 

 scrapers. This frame makes about 20 revolutions a minute and 

 stirs and thoroughly mixes the ground limestone and clay. The 

 thoroughly mixed material is then transferred to a large revolv- 

 ing iron cylinder whose axis of revolution is slightly inclined 

 from the horizontal. The mixture after having been dried " is 

 charged at the upper end of the cylinder and oil or gas fuel blown 

 in at the lower, the gases of combustion passing through the 

 chamber and out at the upper end, while the cement mixture 

 slowly passes down through it, the burned clinker being dis- 

 charged at the lower end." 1 It is very essential that the tem- 

 perature should be regulated, so that the burning may not be 

 overdone, in which case the cement will not " set " properly. The 

 changes produced in burning are, 1) driving off of the mechan- 

 ically combined water, 2) driving off the C0 2 , and 3) fusing to- 

 gether the silica, alumina, lime and iron, all of which except the 

 lime are chiefly obtained from the clay which has been added. 

 The clinker is finally subjected to repeated grindings till it is 

 of the proper degree of fineness, when it is packed in bags or 

 barrels and marketed as " Helderberg " brand of Portland cement. 



Analyses of the limestones used gave the following results. 2 



The clay used in the process was formerly obtained from 

 Howes cave. The accumulation on the floor of the cave repre- 

 sents the impurities left behind during the solution of the lime- 

 stone in the process of formation of the cave. At present the 

 glacial clay from the Cobleskill valley near Howes Cave is used. 



In the Schoharie valley the Manlius and Coeymans limestones 

 have been quarried for lime, for crushed stone and for building 

 purposes. The Manlius was formerly burned in the quarries 

 below Lasell park, but at present no lime is manufactured in this 

 region. Extensive quarrying operations* are however carried on 

 by Messrs Mix & O'Reilly in the northeastern part of the village. 

 Here the Rondout and Manlius are taken out and crushed for 

 road metal. The Coeymans limestone has been quarried for the 



^ies. hoc. cit., p. 711. 



'Eckel, Edwin C. N. Y. State Mus. Bui. 44. apx. p.SGO. 



Manlius .. 

 Coeymans 



Si0 2 CaC0 3 

 1.48 95.75 

 4.12 93.68 



