A little newspaper article that refers to the addressee of your cover:

However, it seems there's a spelling error, as many articles are found with the name "L.A. Mackey", which appears to be the same person. L.A. Mackey, Esq. (1819-1889), (a/k/a Levi Augustus Mackey) actually was President of the Lock Haven Bank in 1857 and was President of the State Normal School, Clinton Co., PA in 1869 and was Mayor of Lock Haven in 1870. In fact, there was even a village (Salona) in Clinton County that was re-named "Mackeyville" in honor of Mr. Mackey who by that time had been elected to Congress.
http://www.findagrave.com/cgi-bin/f...GRid=7765645http://bioguide.congress.gov/script...ndex=M000025