III.—On the Presence of Syenite and Gabbro in Essex County, Massachusetts

Syenite.—Much of the eastern coast of Essex County, Massachusetts, extending from Salem to a point beyond West Manchester, has been found by the writer to be occupied by a typical syenite of a reddish and greyish colour, which in its macroscopic characters appears to be identical with that from Planen'schen Grund, Saxony. The syenite in places contains much biotite, and also, near West Manchester, quartz grains (segregations ?). This syenite is often cut by dykes of a fine-grained greyish syenite, which holds the same relation to the syenite proper as the micro-granite dykes do to the granite of the region, and hence, for convenience of description, the rock of the syenite dykes may be styled micro-syenite