Structure and Rhyme Scheme Analysis

Analyze the structure of the following poem excerpt:

Upon the burning of my son’s body,
When I had cast away the heaviness of despair,
With ashes in my hand, I walked along the shore,
Where the tides pull back and forth, marking time’s wear.

This poem employs a specific rhyme scheme and form that impacts its emotional weight. Considering this structure, what type of form is predominantly used in the poem?