From Port Royal

PlIltADBtfHÍA, Deo. 12. The Bvl'etin ba toe following im portant intelligence : The steamer Donegal rrived this ftfleraoon from the South Atlantic blookading sqwad ron, haviog lefi Port Koyal on the 7th inst. The joint naval and land expeditioD, under Adtniral Denigren and Oen. FoBter, proceeded frorn Buaufort up th Broad Bifer, on Tuesday, December 6, the object beiog to destrov the Poeotaligo bridge, oa the railroad betwenn Charleston and Savannah, The Donogal accornpanied the expedition to Telfany Crek, but did not acoompany it fur'her. Thora were seven gunboats in the expeditioi), and soon after reaohing a proper poaition, a heavy tire was opened by tbem. A foroa waa lacdtíd, and an aotion was coinrnenced before eveuing. Poootilgo bridgo was reaohod and destroyod. Our troops were then entrenched for euch future operations m might be needed. The Doaegal carne down to Port Royal the ame evening, but eould not bring any details of loases on either aide. Of tba suc oesses of the grand object of tho expedition, however, there can be uo doubt. Our ÍDÍormant spesk ia the highent torms of the eDergy and aotivity of Admiral Dahlgren in organizing and directing th raovement of the naval brigade in this affair. When the Doqegal left to coma down the Broad Run, on the evening of the 6tb, ehells were neen flying and exploding, wbich indi cated thtit our forces were determined to drive the anemy out oí any position they rnight hav taken, afcer bnviug been drivec frnro tho bridge. Öeneral Fopter's scouts bad cornmuuicated with General tíherinan'í forcé, which were marchiDg on Savanoab. Th belief was tliüt General Sherman would be in Savannah oo Wednesday, tho 14th Tho Pocotaligo bridge is about thirty five miles from Savanuab. The bridge having been deatroyed, and Sheridan having cut the other railrond cotumunictiori8, Havannah cannot be relieved frora any point north ol that city.