In England the "mark" never appeared as a coin, but as a money of account only, and apparently came into use in the 10th century through the Danes. It first equalled 100 pennies, but after the Norman Conquest equalled 160 pennies = 2/3 of the pound sterling, or 13s. 4d., and therefore in Scotland 31/2d. English.
The mark (merk) Scots comprised a silver coin of this value, issued first in 1570 and afterwards in 1663.
(Original text from the 1911 Encyclopaedia Britannica.)