IN 18th century Orkney and Shetland, the old Norn language was in the last stages of its terminal decline. From the 15th century onwards you see dialects of Scots entering the two places, which developed into 'Shetland Scots' (aka Shetlandic, or Modern Shetlandic Scots) and 'Orcadian', and I would argue that these were the dialects used in the 18th century.

It's not until the 20th century that you see major shifts towards English.