REGIMENTS AND TWO GUNS. NO ROAD WAS LEFT TO ESCAPE BY. I PLACED MY FOUR GUNS IN POSITION, SUPPORTED WITH BUT ONE REGIMENT. WITH THESE I MANAGED TO CHECK THE ENEMY'S ADVANCE IN THE DIRECTION OF AMISSVILLE, BUT THEIR ATTENTION WAS NOW DIRECTED AGAINST THE REAL GUARD, NOW COMPLETELY CUT OFF AND SURROUNDED BY INFANTRY AND ARTILLERY ON THREE SIDES. BY A CIRCUITOUS ROUTE I MANAGED TO CONVEY A MESSAGE TO THEM, AND SUCCEEDED IN CUTTING A ROAD THROUGH A DENSE WOODS, TO ENABLE THE ARTILLERY TO RETIRE. THE ENEMY HAD A LINE OF BATTLE FORMED FOR MILES ON MY LEFT. THIS LINE KEPT ADVANCING, AND, I HAVING NO FORCE TO CHECK HIM, TIME WAS EVERYTHING. TAKING ADVANTAGE OF A TEMPORARY CHECK IN OUR IMMEDIATE FRONT, I SUCCEEDED IN UNITING MY COMMAND, AND WITHDREW DELIBERATELY AND IN EXCELLENT ORDER TO AMISSVILLE, WITH A LOSS NOT EXCEEDING 15. THERE IS NOT A DOUBT BUT THAT AN ENTIRE CORPS WAS IN LINE OF BATTLE AND ADVANCING UPON ME. WE HAVE A PRISONER FROM HILL'S CORPS, WHO WAS TAKEN IN THE FIGHT, WHO STATES THAT A PART OF HIS CORPS WAS THERE ALSO. LONGSTREET WAS CONVINCED THAT 20, 000 MEN WERE ATTACKING HIM. WITHIN ONE MILE AND A HALF OF NEWBY'S CROSS-ROADS WE CAPTURED A SERVANT OF JEF STUART'S MEDICAL DIRECTOR. HE IS VERY INTELLIGENT AND COMMUNICATIVE. HE RAN AWAY FROM THE REBELS AT 9 P. M. LAST EVENING. HE SAW GENERAL STUART AND STAFF AT THAT TIME AT GAINES' CROSS-ROADS, WHERE HE HAD JUST ARRIVED WITH HIS COLUMN. HE HEARD GENERAL STUART GIVE FITZ. LEE ORDERS TO TAKE HIS BRIGADE AND OCCUPY AMISSVILLE. (ONE OF MY REGIMENTS MET HIS ADVANCE, AND DROVE IT TO WITHIN ONE MILE AND A HALF OF GAINES' CROSS-ROADS.) UPON ARRIVING AT GAINES' CROSS-ROADS, GENERAL STUART REMARKED THAT HE WOULD REST AWHILE. THE CONTRABAND STATES THAT STUART'S FORCE HAS BEEN MARCHING EVERY NIGHT FOR ONE WEEK, WITH NOT OVER AN HOUR'S REST EACH NIGHT. STUART PROPOSED PUSHING ON TO CULPEPER LAST NIGHT. I LEARNED TO-DAY THAT A FORCE OF CAVALRY HAD BEEN SEEN MARCHING IN THAT DIRECTION. THE HORSES AND MEN ARE COMPLETELY WORN OUT AND HAVE NOTHING TO EAT. HE ENEMY HAD FEARS OF BEING CUT OFF FROM CULPEPER. THE REGIMENT WHICH I HAVE BETWEEN HERE AND GAINES' CROSS-ROADS HAVE SEEN A CONTINUOUS LINE OF TROOPS PASS SINCE YESTERDAY; ALSO AN IMMENSE TRAIN OF WAGONS. THE LATTER WERE MOVING ON A MORE DISTANT ROAD, PROBABLY THE SPERRYVILLE ROAD. THIS AGREES ALSO WITH THE STATEMENT OF THE CONTRABAND. EWELL'S CORPS IS REBEL ARMY IS MOVING TO CULPEPER AS RAPIDLY AS IT CAN MARCH. ABOUT ONE CORPS AND MOST OF STUART'S CAVALRY HAVE ALREADY PASSED; THE OTHER CORPS ARE STILL IN REAR. A FAMILY HAS JUST APPLIED TO ME FOR A PASS TO GO TO WARRENTON, INTENDING TO GO FROM THERE TO WASHINGTON. THEY LEFT CULPEPER YESTERDAY, AND REPORT NO REBEL TROOPS OF ANY CONSEQUENCE AT THAT POINT, AND MET NONE YESTERDAY ON THE ROAD. THIS SHOWS THAT THE REBEL ARMY HAS NOT REACHED THAT POINT YET. MY HORSES ARE GREATLY IN NEED OF FORAGE. MY SUPPLIES ARE EXHAUSTED. I WILL SEND FOR MY TRAIN TO JOIN ME LOADED AS SOON AS POSSIBLE. I THINK OUR POSITION TO-DAY THE MOST CRITICAL I WAS EVER IN.

VERY RESPECTFULLY, &C.,

G. A. CUSTER, BRIGADIER-GENERAL,

COMMANDING.

MAJOR-GENERAL PLEASONTON.

[P. S.]-I SENT YOU TWO DISPATCHES LAST NIGHT, BUT MY MESSENGERS HAVE NOT REPORTED YET.