Hiere are to bo built immediately four new iron-clud vessela, in addition to tho ten Ei-icssüii guuboats, tlie Ironsidea, Roanoke, and the vessels, the hiying of whose keel-blooks we noriecd ou Weao'éfcday. As far as we cui learn, thcy are to be coustructed as follovys: Otie at Jersey City, ouo at Greenpoint, one :it Boston, and ono at New i'ork. A leadiüg iron-founder of this city, who is now in Washington has telegrapbed to l:is associates in town to erpploy all the availablo meeuantoS they can procure, to build four guts of boilers for new crafts. lt is said that tliere are even moro tlian the number given tó be eomtneneed, but ow ing to a decided disiiidiiiation on the part of Secretary Welk-s imd the constructora to Lave the facts or (Jimensions published, we are couipi'liud to oiuit tliom. The one to bo built at Boston wilt be 240 feet loug, 53 feet beam, and 1,300 tona. The upper deck will beflush, likt; that of the Monitor, neither bulwark or rail risiiig above it. Tlie deck will consist of aix-inch oik plank, witli one a::d lialf inchrs of iron plating oulside of that. Tha iron mail on th out.s'ule of the lmll will be five inches thick Workmen are setting the blocks for this formidable eraft, which will bo built ut ouco in the upper pliipliouso. In this coi)iictitiour it mny not be out of place to mentitm that the tonnage of any of the Monitors bas never yet been priuted.