cover 1852 (1 Jan.) 1c. black on magenta block of four tied by "DEMERARA" double-arc d.s. (dated 7 August 1855) on reverse of 1855 (6 Aug.) entire letter from Mahaica to Georgetown, the face panel shows two strikes of "B G/E 5 C" c.d.s.; the block with very light horizontal fold between. One of the major rarities of British Guiana philately. Friedl Certificate (1979).