A Sea Shell for Vernon Watkins

The words 'unreal' and 'unearthed' suggest that the person the persona is talking about is no longer alive. The persona remembers other poets 'Yeats' and 'David' in the poem. 

'Darkness stayed in a cave' could be a reference to death and how it inhabits in all of us and comes out when it's ready to take us. 

'Others gone also, like you dispensable' could suggest that everyone is equal and that death takes everyone, no matter what their status in life is.