Cape of Good Hope 1891 Robben Island to Cape Town, 1d Letter

1891 Envelope from ROBBEN ISLAND to Cape Town franked with single 1d (SG 49) tied by crisp neat strike of the scarce Robben Island 1864 type cds (Goldblatt CDS3) of MY 28. Cape Town arrival cds on reverse. Scarce postmark, lovely strike. <i>Ex Dillaway.</i>