The position of the Army of the Potomac is critical in the extreme. But several circumstances come to the rescue. It is almost dark. The rebel lines have become inextricably mixed. Colston, who has gradually moved up to Rodes's support, is so completely huddled together with this latter's command, that there is no organization left. Still Jackson's veterans press on, determined to crush our army beyond recovery, and drive it from United-States Ford. Stuart has in fact, at his own suggestion, got orders to move his cavalry division in that direction, and occupy the road to Ely's. A. P. Hill's division is still intact in rear of the two leading lines, now shuffled into one quite unmanageable mass, but still instinctively pushing forward. So faulty have Hooker's dispositions been, in advancing his entire right centre without filling the gap, that the only available troops to throw into the breach, after the rapid destruction of the Eleventh Corps, are Berry's division of the old Third. These hardened soldiers are still in reserve on the clearing, north of headquarters. It is fortunate, indeed, that they are still there; for Sickles has just asked for their detail to join his own column out in the woods, and an hour ago Berry would certainly have been sent. This division is at once thrown across the pike on the first crest below Fairview, west of Chancellorsville. The artillery of the Eleventh Corps is in part re-assembled. Capt. Best, chief of artillery of the Twelfth Corps, has already trained his guns upon the advancing Confederate columns, to protect the new line. But Berry is almost alone. Hays's brigade of the Second Corps, on his right, is his only support. The Excelsior brigade is rapidly pushed into the woods, north of the plank road; the Fourth Excelsior and the First Massachusetts south. Carr's brigade is kept in second line, one hundred and fifty yards in the rear. The men, with the instinctive pride of self-reliance, move up with the steadiness of veterans on drill, regardless of the stream of fugitives breaking through their intervals. The flight of the Eleventh Corps has stampeded part of the Third Corps artillery. But it is re-assembled in short order, and at once thrown into service. Capt. Best manages by seven P.M. to get thirty-four guns into line on the crest, well served. Himself is omnipresent. Dimick's and Winslow's batteries under Osborn, Berry's chief of artillery, join this line on the hill, leaving a section of Dimick on the road. And such part of the disjecta membra of the Eleventh Corps as retains semblance of organization is gathered in support of the guns. Capt. Best has begun to fire solid shot over the heads of Berry's men into the woods beyond; and, as Gen. Lee says, the Confederate advance is checked in front of this crest by the vigorous opposition encountered.