The southern prcss have been very quiet of late conoerning the work upon the Merrimac, but parties who have arrived from Norlolk stnte that she will provo a most daiiirorous customer to any vessel sho may counter. Hundreds of men have boen steadily at work upon her, and sho is believed to be now the most powerful war vtssel afloat in tho American waters. - Her armament is of tho heavieat calibre, her sides pioof against the largest shot, aud, with the formidable ram attached to her, the rebels are very naturally elated with the prospect before thein of " annihilating the Lincoln navy." The Neqro's PjtAYEit. - A Port Royal letter says : " The othor day an old fcllow taken aboard one of the vessels was overheard praying vigoroualy that 1 de Lord would bress these d - d Yankees.' Poor Sambo had never tieard us designated in any othcr way. and gnve the entire title in his prayer.