We have reached the last act in the tragedy of Sunday. It is half-past 4 o'clock. Our front line of divisions has been lost since half-past 10. Our reserve line is now gone, too. The Rebels occupy the camps of every division save that of W. H. L. Wallace. Our whole army is crowded in the region of Wallace's camps, and to a circuit of one-half to two-thirds of a mile around the Landing. We have been falling back all day. We can do it no more. The next repulse puts us into the river, and there are not transports enough to cross a single division till the enemy would be upon us. Lew. Wallace's Division might turn the tide for us--it is made of fighting men--but where is it? Why has it not been thundering on the right for three hours past? We do not know yet that it was not ordered up till noon. Buell is coming, but he has been doing it all day, and all last week. His advance-guard is across the river now, waiting ferriage; but what is an advance-guard, with sixty thousand victorious foes in front of us? We have lost nearly all our camps and camp equipage. We have lost nearly half our field artillery. We have lost a division general and two or three regiments of our soldiers as prisoners. We have lost--how dreadfully we are afraid to think--in killed and wounded. The hospitals are full to overflowing. A long ridge bluff is set apart for surgical uses. It is covered with the maimed, the dead and dying. And our men are discouraged by prolonged defeat. Nothing but the most energetic exertion on the part of the officers, prevents them from becoming demoralized. Regiments have lost their favorite field-officers; companies the captains whom they have always looked to, with that implicit faith the soldier learns, to lead them to battle. Meanwhile, there is a lull in the firing. For the first time since sunrise you fail to catch the angry rattle of musketry or the heavy booming of the field-guns. Either the enemy must be preparing for the grand, final rush that is to crown the day's success and save the Southern Confederacy, or they are puzzled by our last retreat, and are moving cautiously, lest we spring some trap upon them. Let us embrace the opportunity, and look about the Landing. We pass the old log-house, lately post office, now full of wounded and surgeons, which constitute the "Pittsburgh" part of the landing. General Grant and staff are in a group beside it. The general is confident. "We can hold them off till to-morrow; and they'll be exhausted, and we'll go at them, with fresh troops." A great crowd is collected around the building--all in uniforms, most of them with guns. And yet we are needing troops in the front so sorely!