Complex sentence: The parade ground exactness with which the British had set off had now been lost, Sir George Brown turning red with rage, the Russians now faced not with a disciplined British formation, but something with the outward appearance of a mob.
Split into simpler sentences: The parade ground precision with which the British had set off had now been lost. The Russians were now faced, not with a disciplined British formation, but by something with the outward appearance of a mob.