Gunter,
taken from 'Waterloo letters'

This was a letter to his brother, Guy Campbell, note the date.

COLONEL J. CAMPBELL, C.B.
captain and brev.-major 42nd highlanders.
TO MAJOR-GENERAL SIR GUY CAMPBELL, BART.
Liverpool, March 15th, 1838,
MY DEAR GUY, .....
When the 42nd first halted on the road from Brussels, was close to some houses on the left. We moved forward, and soon after turned off to the left and formed line, facing as I have marked on the Plan. I think we were under the rising ground, which I suppose must have been the cornfield with some houses on our right; soon after we were attacked by the Cavalry. We formed square and had some fighting. After we retired in square, still followed by the Cavalry, we halted close to a large farmhouse with a wall round it, and were ordered to lay down. The Artillery were immediately behind on a rising ground, and were firing over us. It was Sir John Elly who told us to lay down.
We formed line, and, I think, advanced, and remained at ordered arms. Many Officers were standing together. Two [were] mortally wounded, and others slightly. You may recollect Gordon, he was shot through the head and lived till next morning. At that time I don't recollect the Regiments near to us. You say the 92nd were in our rear on the road when we were in the cornfield; in that case, we must have fronted different from what I now suppose. As to the position of the Enemy, they appeared in different Columns with an advance of skirmishers. I don't particularly recollect the white house.
When we retired on the 17th and took up our position at Waterloo on the 18th, we were in close column of Regiments. We moved direct to the right, column at half or quarter distance, and returned to the same ground. This movement I think we repeated twice, and were under the fire of the
French Artillery the whole time. Towards evening we formed three or four deep and advanced. The Prussian Cavalry passing through the intervals, perhaps more than a section thrown back, we were not particular as to the exact pivot men, any number according to circumstances. On the 16th, (?)after dark, the French occasionally fired some Guns.......
Yours affectionately,
J. CAMPBELL

I also noted the overhead fire comment.

he doesn't say a great deal and typically seems quite hazy about events.

Mark