Well that is a pity. I had hoped the baptisms would appear in St Merryn but as you have been through the film and Richard and William are not there, I don't know what to suggest. These two baptisms do not appear to be listed elsewhere in Cornwall either. William states in 1851 that he was born in St Merryn and I suspect he is the son of Matthew.
From the Crantock side I am sorry to say I cannot prove a connection, though I am sure it exists. William named his son Cotton. You just don't pull a name like that out of thin air. I had hoped William and Richard may have witnessed each others marriages but no such luck. No Tummons were witnesses.
Richard
TUMMON otp Bachelor = Jane
CARIVECK otp Spinster Crantock by Banns 28 Mar 1809 Both signed (Jane signed Carrivick) Witnesses Mary Jenkin and Ann Carrivick
Banns read Crantock between Richard
TUMMON otp Bachelor and Jane
CARIVICK otp spinster 12, 19, 26 Mar 1809
Richard
TOOMAN of Newquay buried 15 July 1847 Crantock aged 59 years
Now I note in 1841 Richard had a son Matthew which does seem to tie in with St Merryn. I do suspect that Samuel and Cotton are Matthews sons by a previous marriage. Personally I see no reason to tie the American Revolution into this certainly not without proof. (not the sort of reason one would normally see suggested for migration)
People moved for many reasons and there was quite a bit of migration between Cornwall and the North of England. In fact I do see a Samuel TUMMOND was baptised Smeaton Yorkshire WR father Mathew 27 Feb 1774. Unfortunately I do not see a Cotton listed.
Kris
