You should readily find his birth, and successfully go back a further generation or two if you
FIRST: search the death of wife Margaret Cobban, assuming she didn't emigrate.
Margaret's death will be INDEXED under BOTH her surnames. Looking NEXT at the Deaths Register, see whether she was <Wife Of>, or <Widow of> her husband Alexander. That will compress the date range to search for his death, and cut your labour.
Also note WHERE she died. That will compress the location range to search for his death, again cutting your labour.
NOW! go look for the Death of Alexander and note any hits in the Index, that seem interesting. There may be just one, or several. You need to check each of those in the Register, to find the ONE that is correct for your family.
A Death Register entry after 1855, usually has the names of both parents
including the mother’s maiden surname, and the age of the deceased. These
lead fairly successfully, to finding the birth record of the deceased.
The Death entry has other good data, so go get it!
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