LORD MONCK'S ACKNOWLEDGMENT OF AMERICAN INTERVENTION. In acknowledgment of the service rendered by the United States Government in checking the invasion, Lord Monck, the Governor-General of Canada, sent the following despatch to Sir Frederick Bruce, the British Minister at Washington, for presentation to Secretary of State Seward:-- OTTAWA, June 11th, 1866. Sir,--I have learned from the public press the terms of the Proclamation which the President of the United States of America has promulgated against the hostile designs of the Fenians on the Province, the Government of which I have the honor to administer. I have also, by the same means, been made acquainted with the orders issued by the Attorney-General of the United States and other officers of the Administration of that country for the apprehension of the persons of Fenian conspirators and the stoppage and seizure of arms and other supplies intended to be used by them against Canada. As these proceedings of the Government of the United States have materially tended to defeat the hostile purposes of the Fenians against this Province, I shall feel much obliged if you will convey to the Secretary of State for the United States my acknowledgments of the course which has been adopted by that Government in reference to this matter. I have, etc... (Signed) MONCK. LORD MONCK'S REPORT TO THE IMPERIAL GOVERNMENT. In presenting his report to the Right Hon. E. Cardwell, Secretary of State of the British Government, Lord Monck sent the following despatch, which was accompanied by the reports of the Lieutenant-General and other officers who were in command of troops during the campaign:-- OTTAWA. June 14th, 1866. Sir,--I have the honor to transmit for your information, the reports to the Lieutenant-General commanding Her Majesty's forces of the several officers, relating to the proceedings connected with the late Fenian invasion at Fort Erie, Canada West. I think these documents substantially corroborate the account which I gave you from telegraphic and other information in my despatches of the 1st, 4th and 8th instant. From all the information I have received, I am now satisfied that a very large and comprehensive plan of attack had been arranged by the party which is popularly known as the Sweeny-Roberts section of the Fenian Brotherhood. The plan of invasion, in addition to the attempt on the Niagara frontier--the only one which actually occurred--appears to have embraced attacks on the line of the Richelieu and Lake Champlain, and also on the frontier in the neighborhood of Prescott and Cornwall, where I have reason to think the principal demonstration was intended.