Young Lafayette called to day, on his way to New York to embark for France. He left Genl. Washington last Friday perfectly well—and saw a letter from him dated on Saturday afternoon. But on his way, as he drew near to Philadelphia, was told the General was dead.—Mr. Simmons at the War Office told Major Lewis, who just now called to see me, that an Express had passed thro’ Derby with the news. Simmons had it at second hand. It may be true, but is most probably unfounded.