The fine-grained carbonate portion of this formation has a mean grain size between 5 and 15 microns. Further, it is poorly sorted, contains numerous elongate particles, and is associated with ferruginous silt. These attributes are opposed to those ascribed to 'microspar', but are characteristic of mechanically deposited carbonate silt. Calcisiltite is the most appropriate name for such material. Studiesof Recent carbonates show that the comminution of the carbonate skeletal material yields silt-sized carbonate sediment. Abundant fossil debris in the Onondaga shows that such a mechanism could account for the calcisiltite. Most of the calcisiltite is burrowed, and such activity was probably a factor in the disintegration of the shell debris.