Joseph Holt, of Kentucky, late Post-Master General, under President Buchanan, wrote a letter to J. F. Speed upon the policy of the General Government, the pending revolution, its objects, its probable results if successful, and the duty of Kentucky in the crisis. It strikes directly at the heart of treason, and gives it no show of quarter. It vindicates the right of the Federal Executive to send troops into or through any State to suppress rebellion, and rebukes unsparingly the neutral position assumed by the half-hearted Unionists of Kentucky. It shows that the crimes and outrages of the rebels are such as no Government could afford to overlook, and that their pretence that they “want to be let alone” is absurd.--(Doc. 197 1/2.)
The North British Review for this month discussing the future of the United States, says: “There surely cannot be a permanent retrogression and decay in a nation planted in the noblest principles of right and liberty, and combining, in marvellously adjusted proportions, the vigorous and energetic elements of the world's master races, in the midst of which the tone is given and the march is led by that one of them which has never faltered in its onward course, and which is possessed of such tenacity and versatility, that it is everywhere successful. The present calamity and confusion probably form the crucible fire in which the Union is to be ‘purified, made white, and tried,’ in order that she may take her destined place in the van  of the world's progress in Christianity and civilization, fulfilling, in the resistless march of her dominant Anglo-Saxon race across the American continent, one grand part of the Divine scheme for the spread of that Gospel which shall survive all changes, overthrow all evils, and achieve its mightiest triumphs in the later days of our world's history.”
The Charleston Mercury of to-day contains the following :--“Night and day, for the last two months, has the Northern Government been making herculean efforts in its department of war. Preparation on the most gigantic scale has gone on steadily and unflagging, under the intelligent and able superintendence and direction of General Scott. An immense body of volunteers heave been thrown into camp, and are drilling eight ours a day under competent officers of West Point training. The arms at band have been distributed, and all who are to engage soon in battle, have been thoroughly equipped with the best weapons. Factories for the manufacture of cannon, rifles, sabres, bayonets, and ammunition of every description, are in full operation at the North during the whole twenty-four hours of each day. Agents have long since been sent abroad to Europe to procure and forward as fast as possible cargoes of improved arms, and already they lave begun to arrive. Great efforts have also been made for the health, comfort, and supplies of Northern troops. Energy and promptitude have characterized their movements both in Maryland and St. Louis, and their success along the border has so far been complete. They have in the West obtained and secured the great repository of arms for that section, equipped our enemies of St. Louis, Illinois, Indiana, and Ohio, leaving the resistance men of Missouri poorly proivded, Kentucky unarmed and overawed, and Tennessee also, with a meagre provision for fighting, dependent on the Cotton States for weapons of defence. Maryland has been cowed and overpowered, Washington rendered as secure as may be, while Virginia is invaded and Richmond threatened with capture. In all this the military proceedings of the North, since the fall of Sumter, have been eminently wise. For the purpose of overpowering, disheartening, and gaining the first advantages, which, both at home and abroad, are of immense importance, the concentration of all the forces available as promptly as possible, has been clearly the course of generalship and true economy. The first blow is said to be often half the battle. The war policy of Scott and the Northern Government has all the effect of the first blow. The final result we cannot, in the slightest degree, doubt. The immediate signal will depend, in a great measure, upon the number of troops now got ready, and the efficiency of tie preparation made for them by the Confederate Government during the same period Scott has been at work. Let us not commit the mistake of underrating our enemy, or of supposing that, in modern warfare, it is only the courage of a people and the relative military talent of their field-officers that decide the issues of war. Ability in combinations and bravery in executing them may fail of success where the material is wanting or deficient. An hour's delay of a corps of reserve lost the battle of Waterloo; and Napoleon fought the battle with the best troops in the world. They were cut to pieces.”
The United States ship Powhatan captured the Mary Clinton, from Charleston for New Orleans, off the Pass L'Outre, with a full cargo of rice, peas, &c.--New Orleans Picayune, June 1.
Mr W. H. Russell's letters from the South to the London Times, create much comment. According to one dated April 30, the South Carolinians long for “one of the royal race of England to rule” over them.--(Doc. 217.)
The Seventh Regiment, N. Y. S. M., left Washington for New York. It made a fine appearance and received on their departure the same warm eulogium that greeted their arrival.--(Doc. 218.)
The National Intelligencer of to-day contains the correspondence between the bank presidents of the city of New York and the Governor of the State, relative to the proclamation of Governor Brown of Georgia, of the 26th of April last.
The First Regiment of Maine Volunteers left Portland at 8 80 this morning, in a train of eleven cars. They were escorted through the city by the Fifth Regiment, and nearly the whole population. The train left amid the wildest cheering, and a salute from the artillery.--(Doc. 219.)
Ex-Governor Pratt, of Maryland, was arrested this evening at Annapolis, by order of  the Government, and taken to the Washington Navy-Yard.--Boston Transcript, May 81.
At Acquia Creek, 55 miles below Washington on the Potomac, the U. S. gun-boat Freeborn, Capt. Ward, opened fire about 10 A. M., on the ferry-boat Page, lying at the depot of the Richmond, Fredericksburg, and Potomac Railroad. A second round was fired at the depot building, and a third across the bow of the Page. Three batteries on shore, two in the earthwork, near the depot, and a third from the hill above, immediately opened on the Freeborn, when the gun-boat Anacosta came to her assistance. As soon as the vessels had fixed their range they fired with marked effect. The Anacosta took up a position and played upon the depot with rapidity, firing thirteen shells, three of them taking effect and causing much consternation among the rebels. Several of the Freeborn's shells fell into the batteries. The fire from the earthwork batteries ceased in a short time, but a terrific fire was kept up from the main battery on the hill. The boats hauled off at 10 minutes of 12.--(Doc. 220.)