THE PRUSSIANS STILL ADVANCING- Metz in a State of Defense- The Whole Prussian Army in Motion- London Aug 8, 1870- It is authoritatively stated here Prussian troops occupy St. Avoid, and that General MacMahon's corps is in full retreat on Nancy. Frossard's corps was nearly annihilated. Metz has been hurriedly placed in a state of defense and the Emperor's headquarters have been moved to Chalons-sur-Marne.