I3EAI)QUAUnR's AUMV Oï THE PüTOMAC, ) JVlondiiy, Aug. 4. ) Ever sinoe tho firing upon our ship ping at the mU-boat landing by the onuluy's batterics, our troops havo oecupied. the opposito t-bore. Yesterday a recon Dois.sauce was made froru that poiüt back into the country to within f'ourteen miles of Petersburg. It was condueted by Col. Averill, and eomposed of 160 uithe Fifth U. S. and 150 of the Third Pennsylvania Cavalry, with l'our compauies ot' the First Michigan Infantry. - Capts. Castor and Brown, of MoClellan's staif, aecompanied them. At Cox's Mills, five miles from the river, they encountered Cha Tliirtcentli Virginia Cavalry, drawn up in lioe. Our uien oharged on theiii, when they brokc and ruu. - They drovo them to their eneampment at Sycamoro Church, two and a half miles furlhcr, when they again forraed, but werc ingloriouslj; put to fiiglit, leaving behind all thuir tents, camp cquipage and commissary stores, wlneh our troops gathorcd together and burned. The rubols luid two horse killed, six men wounded, and two taken prisoners. Our loss was ono horso killed. After scouriug the country a short distance furthcr, they returned to the river. Tbcra is ni) furthcr evidence of rebel gunboats on tho river this sido of Fm-t Darliug. Information received here goes to show that the new Merrimao wil] not be ready to opérate for three weeks vet. Two of tho gunboiits woro yesterday afternoon engaged in ehelling the opposite shorc above City Poiat. The health of tliu troops has mproved ever since they bngau to receive frcsh vegetalilt's, wliicli wero ordcrcd to bo issucd to tlicm b'y Gou. BicClellvn.