I started Early - Took my Dog
And visited the Sea
The Mermaids in the Basement
Came out to look at me
And Frigates - in the Upper Floor
Extended Hempen Hands
Presuming Me to be a Mouse
Aground - upon the Sands
But no Man moved Me - till the Tide
Went past my simple Shoe
And past my Apron - and my Belt
The ‘Sands’ could be interpreted in many ways. Sand is constantly shifting, like the poet’s imagination.  There is a time progression in this poem; Dickinson starts ‘Early’, so the sands could represent time, as she travels through her imaginative journey. The friendliness of the mermaids is already over taken, Shifting sands represent uncertainty and insecurity.
I Started Early - Took my Dog