Confident that the object of the American general must be to protect the magazines on the Fluvanna, Lord Cornwallis encamped at Elk Island, and advanced his light troops to a position commanding the road, by which it was supposed the Americans must pass. Lafayette, however, discovered in the night a nearer road which had long been disused; and the next morning the British general had the mortification to perceive that the American army had crossed the Rivanna, and taken a strong position behind the Mechunk creek, which, in a great measure, commanded the route leading from the camp of his lordship to Albemarle old court house. At this place a considerable reinforcement of mountain militia was received. [Sidenote: Cornwallis retires to the lower country.] Apprehending the force opposed to him to be greater than it was in reality, and probably desirous of transferring the war to the lower country, Lord Cornwallis abandoned the objects he had pursued, and retired first to Richmond, and afterwards to Williamsburg. [Sidenote: June 18.] The Marquis followed with cautious circumspection. On the 18th of June, he was reinforced by four or five hundred new levies under the Baron Steuben, which augmented his army to four thousand men, of whom two thousand were regulars. That of Lord Cornwallis was, probably, rather more numerous. As the British army retreated to Williamsburg, Lafayette, who sought a partial, though he avoided a general engagement, pressed its rear with his light parties. Colonel Simcoe, who covered the retreat, was overtaken by Colonel Butler about six miles from Williamsburg, and a sharp action ensued. The Americans claimed the advantage; but were compelled to retire by the approach of the whole British army.