ON BOARD STEAMER ARCADIA, April 8, 1863.

Lieutenant-Colonel PETTUS, Comdg. Sunflower Expedition:

COLONEL:

I beg leave to report for your consideration the points along the Sunflower River at which obstructions to the river could be made and earthworks thrown up so as to resist the movements of the enemy in their boats toward the Yazoo River from the Hushpuckanaw or the upper Sunflower. You have doubtless observed that there is but little ground above the overflow along the river bank, and that varying from 1 foot to 6 inches, except where artificial mounds exist, and these are the points I have selected, and shall endeavor to describe, as most suitable for the purpose mentioned.

Mabin's plantation is 19 miles from the mouth of the Sunflower, and on the right-hand side all of this place is under water with the exception of that portion around the dwelling and negro quarters. There are two mounds, one about 100 yards to the left, and the other the same distance in the rear of the house. These mounds are of sufficient height above the overflow to allow of the countersinking of the guns, and are in a commanding position to protect the raft at the point I consider best suited for it. This is about 50 yards below the dwelling. This island would divide the raft into two sections of about 30 yards long each, and to which the ends could be fastened. A large amount of chopping would be required for, say, 500 or 600 yards above the raft, so as to give a field for the play of the artillery. Two rifled 32s would be, I think, sufficient for this point.

The next place I wish to call your attention to is Mound Bayou, which empties into this stream, 78 miles above the head if Little Sunflower. A heavy earthwork could be thrown up here, and as there exist two mounds of considerable size within 100 yards of the river bank, and in open ground, two of the guns commanding this position could be countersunk. The ground at the river bank is 2 1/2 feet above the water, and which increases, I think, a short distance from the river to 4 feet. The river here is from 60 to 75 yards wide, and with an exceedingly swift current. A raft could be thrown across the river below the point where the river turns to the left. This is some 300 yards above the bayou, and 600 yards from the mounds. A battery of four guns could be mounted here to advantage. There is another matter connected with this point as a place of deference. It is below the mouth of the Quiver River some 8 miles, and as it has been reported that there is communication by water between the Tallahatchee and Quiver Rivers, through McNutt's Lake, and likely to be taken advantage of by the enemy, no work of importance could be erected above the mouth of the Quiver until it be ascertained whether or not thealarm through this channel from the enemy's boats.

There is another point very suitable for the deference of the river, some 64 miles above the mouth of Quiver River. On the right-hand bank stand two mounds, one immediately in rear of the order. They are both of nearly the same size, and larger than those at Mound Bayou. They are situated in a small cultivated field, which is from 2 to 3 feet above the overflow. The river is straight for at least three-quarters of a mile, and does not change its course until it reaches a point nearly half a mile above the mounds, where it turns to the left. In the opposite side of the river is a cultivated field, which at present is about 6 inches above the water, and, as it is filled with the old deadened timber, our artillerists might be seriously annoyed by the enemy's sharpshooters. A rifle-pit