The stamp shows Road Town, Tortola anchorage around 1866, at anchor a two-mast topsail rigged schooner, with a rowboat which brings the mail ashore. The schooners were used for the inter-island trade.in the Caribbean.
The depicted topsail schooner is not identified.
More on the topsail schooner is given on:
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British Virgin Islands 1966 60c sg 206, scott?