From The Peninsula

Fortress Monroe, Julv 26 I ara credibly iufonned Ihat Inrgu rebel forcea are beiug con con tra tod on ttm line of the James liiver above the junotioQ of the Appouiatox and James.- They come dowu from liichniomj by the Petersburg and Richmond Kuilroad. I{ is bel.eved tbey already nwn-ber from 50,000 to 60,000, and that Jaekson 3 a cimnmuid of tbeiri, r.otwitlistaiiding illa rumor that he is in pursuit e-f Pope.-. My informant is very eonfident thnt tlio rebels are uow making a bold stand at the above uamed place, and are briugiuir all the forcea therc they ca spnrc trom Richinond. Ho beliefes it is the iutuation of the rebels very soon to inake nu attaok on Suffolk, as they are wittïin twenty miles of tbat city with a considerable forre. Niglit before last a company of rebel cavalry carae down on Gloucester Point, oppoaite Yorktown, seized and ertrried off a lot of coutrabands that bad amunulated there, and also forced into the rebel ariny all the malea that could bo fuund there capable of beaiing tw.aa. Thcj then set fire to a lot of ship tiniber auj left. The rebel cavalry are almost daily prowling about that región, seuking plunder of any kind md pressing into the service all the men they can find who they th ink will bo of any use to them. Similar depredations aro being conimitted in the vicinity of Wllliamsburg, whetber by the guerrillas or ri'gul.irs of the rebel army it is hard to say, as they often go clotlied alike. liy this disguise tley as.sume authority wLiich otherwise they could not. In their masked uborauter they commit many depredations, telling civilians thcy have authority for their actd, being regular confederate cavalry. Yisterday a man obtained a pass ia Norfolk for the pretended purposj of going to Nortfa Carolina. He was watched by an officer and followed several mihs from Norfolk when he took a wrong road and was steering towards fclimuud. - The officer then quieiily rode up, arrestcd him, aud found on hiin two thousand letters he was abut to convey to Riohmond. Il e was taken back to Norfolk and lüdgcd in jail to await bis trial. Ha admitted and states that lie got two dol-, lars apieee for convejing letters botween Norfuik and Iiicluuond. This will stop the avenue by which letters have bütu passed to and froiu Richmond. The stcauier Massacliusetts lias arrivej at Fortrees Monroe from Port lloyal, bound to New York. lic reports all quiet on the South Carolina and Georgk ooasta. ïhe steamsbip South America left Fortress M 00 roe this aftoruoon ladea with co:.trabands. She has gone up tho James liiver.