I think this who you are looking for taken from the memorial inscriptions for Dunscore Village Graveyard.
Sacred to the memory of Francis Blacklock son of John Blacklock who died at Speddoch 3rd September 1822 aged 16 months. Also John Blacklock who died at Tenby, South Wales 6th April, 1836 aged 29 years. Also Thomas Blacklock who died at Dumfries 10th February 1841 aged 26 years. Also George Blacklock who died at Glenriddle 30th January 1847 aged 34 years. Also John Blacklock their father who died at Glenriddle 11th March 1849 aged 71 years. Also Agness McDougal their mother who died at Glenriddle 18th November 1856 aged 78 years. Erected by Robert Blacklock.
There is also another inscription for a William Blacklock who died at Speddoch in 1853 aged 83 years which I can type out if you think it is the same family.
Regards
Morag