An arrest.
--The Frederick (Md.) Citizen states that Thos. H. O'Neal, formerly Secretary of State under Gov. Lowe, was arrested in that city on Thursday, by Lieut. Gilbert, of the Fourth Connecticut Regiment, and conveyed to the barracks by a file of soldiers--Mr. O'Neal had just returned from Flintstone, in Alleghany county, where he had been spending several weeks with his family for the recuperation of his health. The arrest, it is said, was made at the instance of private citizens, who charged him with having correspondence with the Confederate army in Virginia.