A Baltrmoro correspondent, under date oí June 3, says : To render the vast magazine?, seventeen in number, perteetly bomb proof,' the invvard iaoings, which are of heavv graait and brick-work, have been sap-, plied with a walf, formed of bags of Rand, which, ifttr a suitable lrame han boen construc'.ed, are piled wp rn mar. ny successive tier agüinsl it, antil an cncrmous vvidth and thickucss have been attained. The sand is obtained lroin thu interior of the fort, aid tho bage, made oí coarse canvas, are eacli of the capucity of a conp!e of bushels. Thcro ure neavly 499 guns mounted and ready for sorvicö nowy bti !heir calibre is very different from ivfiat it was before. Many of the lighter guna have given place toten inch columbiads, which will throw a ball to a distance of nearly four miles. Much oi the ypaee in the interior of the fort is occupietl by cannon, gun earriages, and long rows oí tents, arranged "with the utmost regurd to order and extra quarters. Within the lust moDth or two thero have been received three cargoes of gun-powder, ono of 35,000 pouuds, anotherof 30,000 pounds, and a thlrtl of 30,000, making 85.000 ponnds in all. To store tliis ainount oí vlllainons saltpetre in the safest manuer has been a vvork oí great labor and skill.