The whole boundary of a finite event may be looked on as a particular example of a vagrant solid as a locus.

Its particular property of being closed prevents it from being definable as an abstractive element.
When a moment intersects an event, it also intersects the boundary of that event.

This locus, which is the portion of the boundary contained in the moment, is the bounding surface of the corresponding volume of that event contained in the moment.

It is a two-dimensional locus.
The fact that every volume has a bounding surface is the origin of the Dedekindian continuity of space.
Another event may be cut by the same moment in another volume and this volume will also have its boundary.

These two volumes in the instantaneous space of one moment may mutually overlap in the familiar way which I need not describe in detail and thus cut off portions from each other's surfaces.