On the morning of the 22d of May last, Major-General Butler, welcomed with a military salute, arrived at Fortress Monroe, and assumed the command of the Department of Virginia. Hitherto we had been hemmed up in the peninsula of which the fort occupies the main part, and cut off from communication with the surrounding country. Until within a few days our forces consisted of about one thousand men belonging to the Third and Fourth Regiments of Massachusetts militia, and three hundred regulars. The only movement since our arrival on the 20th of April had been the expedition to Norfolk of the Third Regiment, in which it was my privilege to serve as a private. The fort communicates with the main-land by a dike or causeway about half a mile long, and a wooden bridge, perhaps three hundred feet long, and then there spreads out a tract of country, well wooded and dotted over with farms. Passing from this bridge for a distance of two miles northwestward, you reach a creek or arm of the bay spanned by another wooden bridge, and crossing it you are at once in the ancient village of Hampton, having a population of some fifteen hundred inhabitants. The peninsula on which the fort stands, the causeway, and the first bridge described, are the property of the United States. Nevertheless, a small picket-guard of the Secessionists had been accustomed to occupy a part of the bridge, sometimes coming even to the centre, and a Secession flag waved in sight of the fort. On the 13th of May, the Rebel picket-guard was driven from the bridge, and all the Government property was taken possession of by a detachment of two companies from the Fourth Regiment, accompanied by a dozen regulars with a field-piece, acting under the orders of Colonel Dimick, the commander of the post. They retired, denouncing vengeance on Massachusetts troops for the invasion of Virginia. Our pickets then occupied the entire bridge and a small strip of the main-land beyond, covering a valuable well; but still there was no occupation in force of any but Government property. The creation of a new military department, to the command of which a major-general was assigned, was soon to terminate this isolation. On the 13th of May the First Vermont Regiment arrived, on the 24th the Second New York, and two weeks later our forces numbered nearly ten thousand.