I think I know how to find Célina Boulé

It occurred to me last night as I was falling asleep that I might be able to use the DNA results to identify Célina Boulé's parents.

It's something of a long-shot, but given this tree:

starting with my grandmother, what we're trying to find is the set of 3rd great-grandparents that's missing.  

All of the DNA matching products try to match you up with distant cousins.   I'm slowly making my way through that list of people, looking at their family trees (when they've bothered to make one) to see if I can find common ancestors, and thereby establish our relationship.   A few have had Alexandre Guimond and Célina Boulé as the common ancestor.

But some of these supposedly "high-confidence" matches appear to have no common ancestors.  This got me thinking - what if the common ancestors are the missing parents for Célina Boulé?  And - how could we identify who they are?

What I need to do is find 4th cousins, determined genetically but NOT through a shared family tree.  Why?  Because if we can identify them through a family tree, then we know they're not Célina's parents.    What we want to find are all the 4th cousins for whom it's not possible to find a common ancestor but that we are certain is on the Québec side of the family (because otherwise they might be one of the unknown Irish or British 3rd great-grandparents).

So:

1.  Are we genetic 4th cousins?
2.  Do our family trees overlap in Québec?   (Or not - see below!)
3.  Do we not see any overlap at the 5th generation?    

Note that this isn't as difficult to confirm as you might think.  There are only three family groups to consider:   a) Narcisse Guimond and Céleste Sévigny,  Basile Tousignant and Marguerite Maillot,  and Pierre Bélanger and Thérèse Maillot.  If none of these families are there, then the only one that remains are the parents of Célina Boulé.   

Nonetheless, for this to work, it still requires one other thing:  Célina MUST have a sibling and my 4th cousin must be a descendant of that sibling.   Otherwise my 4th cousin and I will have the same "hole" in the family tree with Célina being a dead-end.

So - given a set of 4th cousin candidates, under the conditions above, the intersection of all of our family trees' common ancestors should point to the parents of Célina Boulé.   This can get tricky, because it's possible that her parents are already in my family tree through some other route.   If that location in the tree is far away from the 3rd great-grandparent position (i.e., they're also C:9,4's or something) it might still work because the DNA correlation for such a distant cousin would be negligible.  

What if Célina is not Québecois?

One of the likely possibilities is that Célina is adopted and might not have a Québec background!  Instead, it's possible she's an Irish immigrant escaping the Irish potato famine.  There's no evidence to support this but the timing fits, and there was a huge influx of refugees from Ireland in 1847 (at which point Célina would be about 7 years old).  Nearly 100,000 immigrants came though quarantine at La Grosse Île, about 30 miles downstream from Québec before being relocated to Québec, Canada West, and the US:

The mortality rate from a typhus was huge: about 1 in 6 died during, or shortly after the crossing.  So, it's also possible that she was orphaned in this way.     There were programs set up for adoption, typically done by the church, where (usually older) children were placed with families.  It was more of a "foster" system than adoption; the children were seen more as convenient labor than part of the family, and typically kept their original family names.   So Célina might be one of the exceptions: if  - as I suspect - she were adopted/fostered by Moïse Boulé and Domitille Bernier (who do not appear to have had any children of their own), she took on their name (at least some of the time).

(Also, "orphan" has a slightly different meaning in the context of the situation:  some "orphans" had a living parent, but one who was not able to care for them (sickness or destitution) which makes the "adoption" more like foster care.

But her Irishness can be tested too, if there's clearly Québec integration from the late 19th century (i.e., Célina's sibling also married into a Québec family and had children) but the only common ancestors are Irish and never Québecois, then that would lend support to the "Célina is an Irish immigrant" theory.

It doesn't appear there's much in the way of records showing which children were placed with which families.  Another avenue I have not attempted is to see if there are other children that might've been adopted/fostered by Moïse Boulé.  

UPDATE: 8/16/2018

No conclusive results - yet!   But an interesting thing came out of the DNA testing.  According to both Ancestry and 23andMe, my DNA is ~85% British/Irish and ~15% everything else.   Based on the locations of ancestors in my family tree, at the 4th generation, I'd expect that to be more like 75/25, UNLESS Célina is Irish, in which case it becomes more like 81/19 which STARTS to look like the actual results.

That doesn't "prove" anything but it's one more datum that supports the hypothesis.