Entire 1870 Edinburgh to Perth with 2d Blue perf pl13 – interesting contents, excess postage paid

Entire 1870 Edinburgh to Perth with 2d Blue pl13 letter SB tied by Edinburgh duplex stamp dated JU-6-1870, backstamped PERTH JU 7 70 with a quite superb and intact “Royal Bank of Scotland” wax seal with coat of arms. Contents are in relation to credits and debits due to the Perth branch of Royal Bank of Scotland, including a Bill from Union Bank of Australia dated Jun 3 1860 – if additional papers included in this letter, might explain why the extra postage was paid. SG47 used on cover cat £75.