In the course of the forenoon, Lieutenant MASSOW, who had been despatched with a message to the Duke of WELLINGTON, returned with the one from his Grace, communicating the intention of the latter to fall back upon Waterloo and accept a battle there, provided he received the support of two Prussian Corps. (See page 264.) There was every disposition to enter into this proposal, but some degree of uncertainty existed as to whether BÜLOW's Corps would join the Army on the 17th, as also a certain misgiving respecting the Park of Ammunition of both ZIETEN's and PIRCH's Corps, which had been directed upon Gembloux, a circumstance that excited apprehensions as to the possibility of furnishing the much needed supply of ammunition to these Corps which were at hand. In this state of uncertainty, no other resolution could be adopted than that of holding the position in front and in rear of the Dyle (with the Advanced Guard of the Fourth Corps as far forward as Mont St Guibert), until the required ammunition should be obtained; and BLÜCHER deferred replying to WELLINGTON's communication, in the hope that his Army would very soon be relieved from the unpleasant circumstances above mentioned. * * * * * While the Prussians were thus effecting their retreat in good order, along the cross roads of that part of the country (high road there was none), no corresponding activity manifested itself on the part of the French, whom the morning's dawn found still lying in their bivouac. Their Vedettes stood within half a mile of the Columns of THIELEMANN's Rear Guard; the retreat of which, not having commenced until after sunrise, might have been easily remarked: and had the French detached but the smallest Patrol, they could not have failed to discover the direction of that retreat--whether towards Namur or Gembloux. It was not until after THIELEMANN had retired a sufficient distance to escape further notice that any disposition for movement occurred to disturb the perfect quietude of their repose. Then, PAJOL with a Division of his Light Cavalry Corps, under Lieutenant General Baron SOULT, consisting of the 1st, 4th, and 5th Hussars, was detached in pursuit of the Prussians. He struck into the Namur road, and shortly afterwards Lieutenant General Baron TESTE's Infantry Division of LOBAU's Corps (the Sixth), followed in support, and took up a position on the Heights of Mazy.