Interesting, Welch Island is Witch Island!
From 1892 Town and City Atlas Of The State Of New Hampshire. Hurd and Co., Boston.
Supersized image. Click on map to enlarge.
It has been under my nose at the Hollis Library the whole time!
(I still have lots of projects for the fall.)
If you are interested in certain areas, I can zoom in for better detail. Just let me know.