The pale celestite-blue calcite which occurs on the eastern half of Lot 13, Range V, of North Burgess township, Lanark county, Ontario, contains very remarkable lattice-like inclusions of a hydrous magnesium silicate.

The calcite forms crystalline masses belonging to the Grenville series, which has a very extensive areal development in certain parts of Ontario. The texture varies from medium to very coarse, in which the individual cleavage-rhombs of calcite measure one inch or more in diameter. Repeated twinning on e (0112) or (101) is almost invariably exhibited, and is especially pronounced in the more coarsely crystallized varietiea Both the twinning and the crystalline character are results of the very intense metamorphism to which this Archaean limestone has been subjected.